     __________________________________________________________________

   http://invisible-island.net/xterm/
   Copyright © 1997-2019,2020 by Thomas E. Dickey
     __________________________________________________________________

   Here is the latest version of this file.

                   XTerm – Frequently Asked Questions (FAQ)

     * (top)
     * What is XTerm?
     * Who wrote XTerm?
     * What is a VT220?
     * What platforms does it run on?
     * What is the latest version?
     * What versions are available?
     * Comparing versions, by counting controls
     * How do I ...
     * Frequent problems
     * Known Bugs in XTerm and Look–alikes
     * How do I build XTerm?
     * How do I report bugs?
     * Additional Information
     * Ongoing/future work

What is XTerm?

   From the manual page:

     The xterm program is a terminal emulator for the X Window System. It
     provides DEC VT102/VT220 and selected features from higher-level
     terminals such as VT320/VT420/VT520 (VTxxx). It also provides
     Tektronix 4014 emulation for programs that cannot use the window
     system directly. If the underlying operating system supports
     terminal resizing capabilities (for example, the SIGWINCH signal in
     systems derived from 4.3bsd), xterm will use the facilities to
     notify programs running in the window whenever it is resized.

   That is, xterm (pronounced "eks-term") is a specific program, not a
   generic item. It is the standard X terminal emulator program.

   This FAQ presents various useful bits of information for both the
   specific program as well as other programs that imitate it.

   As a stylistic convention, the capitalized form is "XTerm", which
   corresponds to the X resource class name. Similarly, uxterm becomes
   "UXTerm".

Who wrote XTerm?

   I've been working on xterm since early 1996 (see my changelog for
   details).

   But the program is much older than that.

  A Prehistory Perspective

   A lot of people, cited at the bottom of the manual page wrote the
   original xterm program, maintained by the X Consortium (later part of
   The Open Group – I'm well aware of the distinction, but am citing when
   the work was done, not who the current owner may be). There is no
   changelog, and it is not clear who did what. Email from Jim Gettys
   (September 1998) provides some background:

     Cast of thousands...

     To give a bit of history, xterm predates X!

     It was originally written as a stand-alone terminal emulator for the
     VS100 by Mark Vandevoorde, as my coop student the summer that X
     started.

     Part way through the summer, it became clear that X was more useful
     than trying to do a stand alone program, so I had him retarget it to
     X. Part of why xterm's internals are so horrifying is that it was
     originally intended that a single process be able to drive multiple
     VS100 displays. Don't hold this against Mark; it isn't his fault.

     I then did a lot of hacking on it, and merged several improved
     versions from others back in.

     Notable improvements include the proper ANSI parser, that Bob
     McNamara did.

     The Tek 4010 support came from a guy at Smithsonian Astrophysical
     Observatory whose name slips my mind at the moment.

     Ported to X11 by Loretta Guarino.

     Then hacked on at the X Consortium by uncounted people.

   There is a git repository here which gives some more of xterm's
   prehistory.

   Email from Doug Mink (October 1999) provides more background:

     I was checking out the newly revised AltaVista search engine to see
     what was on the net about xterm, and I found your pages. I can add
     to the FAQ in that I was the "guy at the Smithsonian Astrophysical
     Observatory" Jim Gettys refers to. I am listed at the end of the man
     page under authors. What happened was that I was hired by SAO (after
     leaving the research staff at MIT) in October 1985 to write analysis
     software for the Spacelab 2 Infrared Telescope which was to fly on
     the Space Shuttle in 1985 less than six months after I was hired. I
     came with a tar tape full of software I had written for Unix and
     Tektronix terminals, but I was presented with a VS100 terminal which
     had an early version (X6 or so) of xterm, with no graphics
     capabilities. SAO is at Harvard, across Cambridge from MIT, where
     Jim Gettys was detailed from DEC to the X project, and Jim had
     connections with SAO, having worked here after college (MIT, where
     we had both worked at the observatory at various times); he was
     still sharing an apartment with an SAO colleague of mine, too.
     Anyway, everyone decided that since I knew Tektronix commands pretty
     well, and our group desparately needed the graphics capabilities, it
     would be a good use of my time to implement a Tektronix terminal
     emulator under X. So I set to work learning more C--I had only
     written a couple of wrappers to C I/O routines so I could use them
     with my Fortran software--and wrote a Tektronix emulator. The only X
     documentation at the time was the code itself. While I was at it, I
     wrote an improved Tektronix emulator for our Imagen laser printer
     which used the full resolution of that 300 dpi printer instead of
     the effective 100 dpi (i.e. jaggy) emultator distributed with the
     printer. The original xterm Tek emulator shared a window with the
     VT100 emulator, much like on the VT240 terminals which I had been
     using at MIT before I came to Harvard. With a VAX 750 running
     several VS100's, window creation was sloowww, so sharing a window
     was the quickest way to do things, and all of my software was
     written for that mode of operation, anyway. While I wrote the
     emulator so that my software would work on it, it was tested by the
     X group against a BBN graphics package, the name of which slips my
     mind right now.

     Anyway, 15 years later, I am still using xterm and some of the same
     mapping software I wrote the emulator for. And I am still at the
     Smithsonian Astrophysical Observatory.

  My Involvement

   My involvement with xterm through XFree86 began at the end of 1995.
   This website has been "here" since 2001/6/5, replacing my ClarkNet
   page. I started the ClarkNet page 1996/12/31, as a followup to the
   release of ncurses 4.0) which featured xterm as one of the 16 programs
   I was involved with. From the outset, the page provided a link to a
   snapshot of the current source. Copies of patches which I sent to
   XFree86 were available on the ftp area.

   XFree86 had its sources in CVS, but (like others in that era), were not
   directly visible to random developers. That came later. I started by
   downloading the sources (30Mb of compressed tar-files on a 56Kb phone
   connection took about 6 hours) and updating them with patches from the
   XFree86 mailing list.

   Like the other programs that I worked on with others (vile, tin, lynx),
   I set up an RCS archive to track my changes locally before sending
   patches to the development list. As the XFree86 developers issued new
   patches, I would re-synchronize my archive. Later, XFree86 provided CVS
   (initially readonly). I was granted commit privileges on this in
   November 2000, and stopped mailing patches after #149.

   Throughout this period, my work on xterm was released as part of
   XFree86. It was rare for a separate package to be provided. That was
   due to the potential conflict between the install procedures. Users of
   the downloads from my web/ftp site were predominantly individual
   developers.

   There were exceptions. Christian Weisgerber proposed a package for
   FreeBSD ports later in 1999 (ports/15545: new port: x11/xterm, followup
   in March 2000). However, that was an exception. None of the Linux
   distributions provided a separate package before 2003 (when Mike Harris
   created a package of patch #177 for Red Hat). Again that is more of an
   exception than a rule:
     * SuSE's package began October 23, 2004 with patch #196.
     * Mandriva's package began October 22, 2005 with patch #205.
     * The Debian package for xterm began in January 6, 2006 with patch
       #204.

   Given that context (sources distributed via XFree86 CVS, releases via
   XFree86), the statement made by an Xorg hacker early in 2005 asserting
   that “It has not been maintained by anyone within the XFree86 or X.org
   trees for many years” was at best misleading.

   After the “fork” (sic) of Xorg in 2004, I continued to commit changes
   for xterm in XFree86 CVS until patch #216 in mid-2006. I stopped at
   that point because it was not possible to incorporate changes into
   xterm which were not sent to me first. I still send patch announcements
   to both the XFree86 and Xorg mailing lists, of course.

   At that point (mid-2006), the XFree86 CVS was no longer the primary
   development repository for xterm. My RCS archive filled that need.
   Later (starting in 2016), I provided Git snapshots using the RCS labels
   which I make in development:
     * Old xterm patches, from patch #1 through patch #149.
     * Git snapshots, starting from xterm patch #41

  Focus of this FAQ

   This FAQ is oriented toward the version of xterm originally distributed
   with XFree86 (more commonly known as modern, or "new xterm", with a
   corresponding terminal description "xterm-new"), which was based on the
   X11R6.3 xterm, with the addition of ANSI color and VT220 controls.

What is a VT220?

     * Why a VT220?
     * What is a State Table?
     * Why not emulate VT320?
     * Why emulate VT420?
     * Why not emulate VT520?

  Why a VT220?

   The manual page mentions a VT220. Most terminal emulators documentation
   talk about VT100. But a VT100 is a rather limited subset of what people
   expect:
     * VT100s have no function keys. Arguably, PF1-PF4 are function keys.
       My keyboard has 12 function keys.
     * VT100s do not do color.

   Initially, I was only interested in making colors workable for curses
   programs.

   Later, I noticed that xterm had some support for what would now be
   termed as ISO-2022. That was a VT220 feature which preceded ISO-2022
   called National Replacement Character sets. In any case, it was not a
   VT100 feature. There were some missing pieces. So I decided to fill in
   those pieces and make xterm a VT220 emulator. (VT220s do not do ANSI
   color either—the missing pieces were in other areas).

   XTerm also provides features that are in neither VT100 nor VT220, which
   are used by other programs as "xterm emulation".
     * set (and retrieve) window- and icon-labels using escape sequences.
     * interpret mouse clicks as escape sequences that can be read by a
       program.

   By the way, the control string used for setting the titles was not in a
   standard format:
     * In X10 (1988), the string was simply terminated by any nonprinting
       character.
     * X11R4 (1989) modified that to ensure that the nonprinting character
       is an ASCII BEL (control/G).
     * There is no explanation in the (sketchy) notes distributed with the
       X11R4 xterm; in retrospect it seems that the most likely
       explanation for the choice is that it was simpler to implement in
       shell scripts than ESC \.

   ECMA-48 (the standard) does not describe this particular control, but
   prescribes its format (an operating system command). It does not use a
   BEL.

   I revised that area starting in 1996,
     * first to use xterm's state table for handling the input, and then
     * to accept the standard string terminator as well.

   In addition to implementing the VT220's National Replacement Character
   sets (see vttest screenshots), I added other features to emulate the
   successive models of DEC terminals. The decTerminalID resource (in
   1996) lets users select the emulation to use. Because many of my
   changes were extensions (features not in any of DEC's terminals) and
   because well-behaved VT100 applications would not use features from
   higher-level terminals it was not initially important to prevent use of
   those by applications which assumed they were using just a VT100.
   Knowledgable users could easily configure xterm to emulate a VT220. In
   2012, I changed the default from VT100 to VT420.

  What is a State Table?

   That was mentioned regarding the title strings. XTerm uses a state
   machine to handle incoming characters. That is essentially what a real
   terminal does. Other "xterm" terminal emulators typically do not do
   this, which makes them not do well with vttest.

  Why not emulate VT320?

   You could do that (by changing decTerminalID, but the results were not
   that interesting). In retrospect, the VT320 was a stopgap
   implementation designed to bridge between the VT200 series and the
   VT420. It provided a standard codepage (for ISO Latin-1).

   While it had other features not found in the VT200-series, most of
   those are less useful in a terminal emulator. I did adapt the ECMA-48
   scrolling operations which the VT320 interpreted as panning the visible
   display in the terminal's memory. Expect some difference there (if you
   can find an application on VMS which used the feature).

   The VT320 was popular with developers of commercial terminal emulators,
   whose literature referred to it as supporting ANSI color. It did not do
   this.

  Why emulate VT420?

   The VT420 was interesting because it provided two features that could
   be useful:
     * rectangles
     * left/right margins (like the top/bottom scrolling margins)

   A VT420, of course, supports all of the features in VT320, in turn all
   of the features in VT220, and in turn VT100. Users would not lose
   features by changing the default emulation to VT420. By changing the
   default emulation, most users would automatically be able to use
   applications (such as tmux) that could perform better if the left/right
   margin feature is available. I changed the emulation to VT420 in 2012
   for this reason.

   XTerm does not emulate some esoteric features (such as dual sessions)
   because those require hosts using special software, and no
   publicly-available documentation was available.

  Why not emulate VT520?

   Again, the VT500-series is less interesting because most of the
   features which are not hardware-specific (such as reporting
   transmission rate) are less useful.

   However:
     * the VT500-series provides additional codepages (like the VT320).
       XTerm does that.
     * the VT500-series supports some of the ECMA-48 cursor-movement
       operations which had been overlooked in the previous terminals.
       XTerm does that (based on ECMA-48 itself, and later on DEC's
       documentation).

   As for the other features, most are not useful in emulation (since they
   are hardware-specific). Additionally, these less-used features are not
   documented precisely and since the only point of providing them would
   be for successful interoperability with legacy applications, some
   reverse-engineering would be needed to provide a faithful emulation. To
   date there are no known terminal emulators which do that.

What platforms does it run on?

   XTerm runs in all of the implementations of X11. As of 2000, I had
   built and run these since I started working on xterm in 1996:
     * AIX 3.2.5, 4.1, 4.3 (cc)
     * Digital Unix 3.2, 4.0, 5.0 (cc)
     * FreeBSD 2.2.6 to 6.0 (gcc 2.8)
     * HP-UX 9.05 to 11.23 (gcc 2.7.2 to 3.4)
     * IRIX 5.2, 6.2 (cc, gcc 2.7.2, gcc 2.8)
     * Linux 2.0.0 to 2.6.26 (gcc 2.7.2 to 4.3)
     * SCO OpenServer 5 (cc, gcc).
     * Solaris 2.4, 2.5, 2.5.1, 2.6, 7, 8 (cc, gcc 2.7.2)
     * SunOS 4.1.1, 4.1.3 (gcc 2.7.2)

   The older configurations have X11R5 libraries. Only minor changes are
   needed to make xterm work on those systems. However, X11R6 provided
   better locale support, as well as new features such as the active icon.
   X11R7... not much to say there.

   Since 2000, there have been many changes (including new platforms such
   as MacOS, NetBSD, OpenBSD, etc., as well as QNX, Cygwin, and Minix).

What is the latest version?

   The most recent (and well supported) version of xterm is the one that I
   maintain:
     * current source (ftp)
     * current source (http)

What versions are available?

   There are several other versions of xterm, based on xterm's source.
   These include
     * ansi_xterm
     * color_xterm
     * cxterm (Chinese)
     * hanterm (Korean)
     * mxterm
     * nxterm
     * kterm (Japanese)
     * xterm (from X Consortium)

   There are similar programs not based on xterm's source, which are
   compatible to different degrees. These include
     * dtterm
     * emu (from X Consortium)
     * Eterm
     * GNOME Terminal
     * Multi GNOME Terminal (MGT)
     * mterm
     * konsole
     * mlterm (Multi Lingual)
     * osso-xterm
     * roxterm
     * rxvt
     * st
     * xfce-term
     * xgterm
     * xiterm

   Some of these use the VTE widget. Since that supplies most of the
   terminal emulation, the remaining differences between programs using
   VTE tend to be at the level of the window manager (menus, borders,
   etc.). Other (older) programs which are based on reusable widgets
   include dtterm and emu.

   (I am aware of a few others, such as xcterm, but have not seen a
   working version of these).

   Finally of course, there are a multitude of programs which set TERM to
   "xterm", in the hope that applications will treat them the same as
   xterm. For example,
     * PuTTY does this (see its FAQ A.5.1 What terminal type does PuTTY
       use?). But its wrapping behavior is incompatible with xterm (and
       any vt100 emulator). You can see this in the first menu entry for
       vttest.
     * VTE does this. But consider the list of problems with VTE and with
       GNOME Terminal. The attitude of the developers is that by copying
       from xterm, they are entitled to do this whether or not the program
       actually matches xterm's terminal description. This is unchanged
       since the mid-2000s (see Debian #368916 for example).
     * Konsole does this as well—intentionally as shown in KDE #145977 –
       Konsole has a terminfo entry of its own; please change default
       $TERM. The reasoning expressed there is that Konsole "should" match
       xterm. Incidentally, one of the comments (about xterm's support for
       mouse) cited as proof a page about Gpm from Linux Journal which was
       more than 12 years old.

   Each of the programs noted here which are well-established and which
   are known to differ markedly from xterm have their own terminal
   descriptions in ncurses, to which TERM should be set. Otherwise,
   bug-reports are misdirected to ncurses which should have been addressed
   by the respective developers of these programs. These include
     * Eterm
     * gnome (obsolete)
     * konsole
     * mlterm
     * mrxvt
     * putty
     * rxvt
     * st
     * vte (preferred)

Comparing versions, by counting controls

   Several of these programs are claimed (either by their developers, or
   their users) to emulate "most" of xterm. To me, "most" would be
   something quantifiable, e.g., 80 percent. To satisfy my curiousity, I
   wrote a script to extract the control sequence information from
   ctlseqs.txt. This counts each control sequence, as well as the
   variations such as setting bold, color, inverse video. Then I
   (laboriously) inspected these terminal implementations:
     * xterm patch #266 ("xterm-new")
     * X11R6.3 xterm (xterm-r6)
     * DEC vt220
     * DEC vt102
     * rxvt 2.7.10
     * rxvt-unicode 9.09 (urxvt)
     * konsole 2.5.3
     * VTE 0.25.91 (vte), used in GNOME-Terminal and kindred.

   As of mid-November 2010, these were the latest implementations. I
   included data for the vt220 and vt102 to be able to contrast the
   various terminal emulators against those as well as xterm. There were:
     * 498 control sequences listed in the corresponding file for xterm
       patch #266.
     * 192 of those are "primary", e.g., disregarding parameters such as
       those distinguishing bold from color.
     * 37 of the primary control sequences have secondary sequences.

   For each control, there are three possibilities:
    1. "yes" — the terminal implements it, matching xterm. If xterm
       implements it, and it is a feature of vt220 or vt102, then in turn
       xterm's behavior must match vt220 or vt102.
    2. "partial" — the terminal implements it, but its behavior does not
       match the reference noted above.
    3. "no" — the terminal does not implement the control.

   The control sequences document lists a few controls which xterm does
   not (completely) implement, e.g.,
     * key-repeat
     * enabling LEDs other than scroll-lock

   None of the other terminal emulators implements those either.

   CAPTION: Comparing against the control sequences document

   yes partial no   program
   488 4       6   xterm-new
   154 6       338 xterm-r6
   188 5       305 vt220
   104 0       394 vt102
   204 3       291 rxvt
   219 3       276 urxvt
   191 2       305 putty
   170 3       325 konsole
   184 6       308 vte

   Modern xterm implements 188 primary controls. In this table, vte ranks
   lower than PuTTY because it does not support vt52 emulation. This is
   not unusual, since the rxvt-based emulators do not, either. However,
   all vt100's provide this feature; programs lacking this are not really
   a vt100 emulator. On the other hand, PuTTY (which is not a vt100
   emulator due to its incompatible wrapping behavior) supports this
   feature.

   Aside from that, the various emulators implement much the same features
   from xterm. None implements as many as half of xterm's controls.

   CAPTION: Comparing against xterm

   yes partial no   program
   488 0       0   xterm-new
   154 6       328 xterm-r6
   182 2       304 vt220
   98  0       390 vt102
   204 3       281 rxvt
   219 3       266 urxvt
   189 2       297 putty
   170 3       315 konsole
   184 6       298 vte

   DEC VT220 implements 96 primary controls. Modern xterm (as documented),
   implements most of the VT220. VTE implements fewer than half. The
   others are a little better. None of the others could be used as a real
   VT220.

   CAPTION: Comparing against vt220

   yes partial no   program
   182 0       6   xterm-new
   78  6       104 xterm-r6
   188 0       0   vt220
   104 0       84  vt102
   101 3       84  rxvt
   106 3       79  urxvt
   107 2       79  putty
   100 3       85  konsole
   88  6       94  vte

   DEC VT102 (the actual flavor used for "vt100" in most cases),
   implements 68 primary controls. Again, VTE fares worst, and the others
   a little better.

   CAPTION: Comparing against vt102

   yes partial no  program
   98  0       6  xterm-new
   70  6       28 xterm-r6
   104 0       0  vt220
   104 0       0  vt102
   79  2       23 rxvt
   81  2       21 urxvt
   86  2       16 putty
   85  3       16 konsole
   60  1       43 vte

   I have continued to add features to xterm:
     * as of September 2013, it implemented 546 of 556 documented controls
     * as of October 2019, xterm implemented 713 of 723 documented
       controls.

   The other programs change far more slowly. As a result they implement a
   smaller fraction of xterm's repertoire in 2019 than in 2010. Even for
   cases where they implement a function, it may not work properly (see
   for example the screenshot of VTE in the vttest NRCS examples).

   In summary, none of the other terminal emulators emulates "most" of
   xterm. Instead, they implement the most commonly-used control
   sequences, and there are differences between them.

How do I ...

   Not really problems, but frequently asked questions (the point of this,
   after all):
     * How do I change the font size?
     * How do I print the screen?
     * How do I set up function keys?
     * How do I set the title?
     * How do I make the cursor blink?

  How do I change the font size?

   XTerm uses fonts given as resource settings. You can switch between
   these fonts at runtime, using a menu. This is documented in the
   manpage, in the MENUS section.

   X Consortium xterm provides popup menus, by pressing the control key
   together with the mouse button. Control right mouse button pops up the
   VT FONTS menu, from which you can select fonts that are specified in
   xterm's resources. Usually these are in increasing order of size.

   Modern xterm provides the menu, plus a feature adapted from rxvt:
   pressing the shifted keypad plus or minus keys steps through the font
   menu selections, in order of their size.

   XTerm's manpage does not document the syntax for X resources; it is
   done in the X documentation. If you are instead asking about a problem
   displaying a given font, it may be due to a problem with your resource
   settings.

  How do I print the screen?

   That depends on why you want to print it.

   If you want a trace of an interactive session, you should use the
   script program. It records every character sent to the screen,
   recording them in a file typescript. There are two drawbacks to this
   approach:
     * Every character is recorded. Even cursor movement, if you run an
       editor.
     * You must start a new shell to capture the typescript file.

   Well, what about logging? Some versions of xterm support logging to a
   file. In fact modern xterm does. Logging was dropped from X Consortium
   xterm during X11R5 due to security concerns. Those were addressed, but
   logging was not reinstated (in fact there is a related bug in xterm).
   Some people prefer this, because it is convenient: you can start and
   stop logging a popup menu entry. However
     * Every character is recorded. Even cursor movement, if you run an
       editor.
     * Line drawing characters are translated to control characters, i.e.,
       codes 0-31 (this may be fixed sometime, it is a problem inherited
       from X Consortium xterm).

   Both script and logging are useful for recording, but they require
   interpretation to make sense of the trace. You probably would not send
   that trace to a printer (not twice, anyway).

   If you want to print the contents of the screen, modern xterm
   implements, as part of the VT100 emulation, an "attached" printer.
     * The printer is really a pipe command, to which xterm writes.
     * You can print the current line, page, or continuously with the
       corresponding control sequences. That takes an application program
       which knows how to print the screen.
     * If you do not have an application, xterm has a popup menu entry to
       print the window.

   There are limitations and tradeoffs using the "attached" printer,
   because it is an emulation:
     * The emulation is based on detailed documentation for a VT320. This
       states that control sequences are sent in each line to reset bold,
       underlining and other printable attributes, and to set them as
       needed. Your printer probably does not understand this sort of
       input. Use the xterm resource printAttributes to get more easily
       printed output.
     * The printer may hang. Not really, but it seems that way. If you use
       the "attached" printer from an application designed for the VT100
       terminal, it is written with the assumption that the printer is a
       dedicated piece of hardware, printing onto a continuous form. Use
       the printerAutoClose resource to change xterm's behavior to close
       the printer pipe whenever the terminal is told to switch the
       printer offline.

   If you use the popup menu to print the screen, this will close the
   printer pipe unless it was already opened by the application running in
   xterm.

  How do I set up function keys?

   With modern xterm, this is relatively simple. So I'll answer that
   first.

   With X Consortium xterm, you had partial support for DEC VTxxx function
   keys. Function keys F1 to F12 correspond to DEC's F1 to F12 (sort of).
   Actually, DEC's VT220 terminals do not have codes for F1 through F5.
   They are reserved for local functions. And the VT220 (and up) terminals
   have 20 function keys. So you cannot do anything with the F13 through
   F20 (i.e., DO, HELP and SELECT). Finally, though xterm is reputed to be
   VT100-compatible, it has no support for the VT100 keypad (PF1 to PF4,
   and the "," key).

   Modern (XFree86) xterm changed the X Consortium codes for F1 to F4 to
   match the VT100 PF1 to PF4, except when the emulation level is VT220
   and up. In this case, it generates the same F1 to F4 codes as X
   Consortium xterm. Moreover, it adds a new resource sunKeyboard, which
   tells the program whether it has only 12 function keys (i.e., a Sun or
   PC keyboard). If so (this is selectable from the popup menu), you can
   use the control key with F1 to F12 to get F13 to F24, and use the "+"
   key on the keypad as an alias for "," (comma).

   The emulation level for modern xterm is set via the resource
   decTerminalID, e.g., to 220 for a VT220. Once set, applications can set
   the emulation level up or down within that limit. DEC's terminals are
   configured in much the same way by a setup option.

   That is the simple way, using a couple of new resources. The
   traditional way to get function keys involves translations. I have seen
   a few postings on the newsgroups that do this. Here is one from Bruce
   Momjian <root@candle.pha.pa.us> for a VT220:

     xterm $XTERMFLAGS +rw +sb +ls $@ -tm 'erase ^? intr ^c' \
             -name vt220 -title vt220 -tn xterm-220 "$@" &

   with the corresponding resources:

     XTerm*VT100.translations: #override \n\
             <Key>Home: string(0x1b) string("[3~") \n \
             <Key>End: string(0x1b) string("[4~") \n
     vt220*VT100.translations: #override \n\
     ~Shift  <Key>F1: string(0x1b) string("OP") \n \
     ~Shift  <Key>F2: string(0x1b) string("OQ") \n \
     ~Shift  <Key>F3: string(0x1b) string("OR") \n \
     ~Shift  <Key>F4: string(0x1b) string("OS") \n \
     ~Shift  <Key>F5: string(0x1b) string("[16~") \n \
     ~Shift  <Key>F6: string(0x1b) string("[17~") \n \
     ~Shift  <Key>F7: string(0x1b) string("[18~") \n \
     ~Shift  <Key>F8: string(0x1b) string("[19~") \n \
     ~Shift  <Key>F9: string(0x1b) string("[20~") \n \
     ~Shift  <Key>F10: string(0x1b) string("[21~") \n \
     ~Shift  <Key>F11: string(0x1b) string("[28~") \n \
     ~Shift  <Key>F12: string(0x1b) string("[29~") \n \
     Shift   <Key>F1: string(0x1b) string("[23~") \n \
     Shift   <Key>F2: string(0x1b) string("[24~") \n \
     Shift   <Key>F3: string(0x1b) string("[25~") \n \
     Shift   <Key>F4: string(0x1b) string("[26~") \n \
     Shift   <Key>F5: string(0x1b) string("[K~") \n \
     Shift   <Key>F6: string(0x1b) string("[31~") \n \
     Shift   <Key>F7: string(0x1b) string("[31~") \n \
     Shift   <Key>F8: string(0x1b) string("[32~") \n \
     Shift   <Key>F9: string(0x1b) string("[33~") \n \
     Shift   <Key>F10: string(0x1b) string("[34~") \n \
     Shift   <Key>F11: string(0x1b) string("[28~") \n \
     Shift   <Key>F12: string(0x1b) string("[29~") \n \
             <Key>Print: string(0x1b) string("[32~") \n\
             <Key>Cancel: string(0x1b) string("[33~") \n\
             <Key>Pause: string(0x1b) string("[34~") \n\
             <Key>Insert: string(0x1b) string("[2~") \n\
             <Key>Delete: string(0x1b) string("[3~") \n\
             <Key>Home: string(0x1b) string("[1~") \n\
             <Key>End: string(0x1b) string("[4~") \n\
             <Key>Prior: string(0x1b) string("[5~") \n\
             <Key>Next: string(0x1b) string("[6~") \n\
             <Key>BackSpace: string(0x7f) \n\
             <Key>Num_Lock: string(0x1b) string("OP") \n\
             <Key>KP_Divide: string(0x1b) string("Ol") \n\
             <Key>KP_Multiply: string(0x1b) string("Om") \n\
             <Key>KP_Subtract: string(0x1b) string("OS") \n\
             <Key>KP_Add: string(0x1b) string("OM") \n\
             <Key>KP_Enter: string(0x1b) string("OM") \n\
             <Key>KP_Decimal: string(0x1b) string("On") \n\
             <Key>KP_0: string(0x1b) string("Op") \n\
             <Key>KP_1: string(0x1b) string("Oq") \n\
             <Key>KP_2: string(0x1b) string("Or") \n\
             <Key>KP_3: string(0x1b) string("Os") \n\
             <Key>KP_4: string(0x1b) string("Ot") \n\
             <Key>KP_5: string(0x1b) string("Ou") \n\
             <Key>KP_6: string(0x1b) string("Ov") \n\
             <Key>KP_7: string(0x1b) string("Ow") \n\
             <Key>KP_8: string(0x1b) string("Ox") \n\
             <Key>KP_9: string(0x1b) string("Oy") \n

     !       <Key>Up: string(0x1b) string("[A") \n\
     !       <Key>Down: string(0x1b) string("[B") \n\
     !       <Key>Right: string(0x1b) string("[C") \n\
     !       <Key>Left: string(0x1b) string("[D") \n\

     *visualBell:    true
     *saveLines:    1000
     *cursesemul:    true
     *scrollKey: true
     *scrollBar: true

   Note that real VT220 terminals use shifted function keys to mean
   something different: the user-programmable keys (i.e., DECUDK). Modern
   xterm supports this, but the translations do not (they're using shift
   to select F13 to F20).

   Here's another one, from Robert Ess <ress@spd.dsccc.com>:

     #!/bin/sh

     #               vax
     # 09-17-96      Bob Ess      - initial creation
     # 09-26-96      Shig Katada  - Additional keybindings
     #
     #               Script file to incorporate keybindings and command l
     ine
     #               options for connecting to a VAX node

     # Usage statement
     Usage(){
             echo
             echo " Usage  : vax -options"
             echo
             echo " Options: -80   for 80 column terminal"
             echo "          -132  for 132 column terminal"
             echo "          -fg colorname"
             echo "          -bg colorname"
             echo "          -fn fontname"
             echo "          -fb bold fontname"
             echo "          -host [altair] [devel] [leonis] [castor]"
             echo ""
             echo " Example: \"vax -80 -fg white -bg black -fn 9x15 -fb 9
     x15b -host castor\""
             echo "          Starts a VAX session with an 80 column termi
     nal"
             echo "          with a black background, white foreground, a
      normal"
             echo "          font of 9x15 and a bold font of 9x15b, and c
     onnects"
             echo "          to the node 'castor'"
             echo
             echo "          If you need additional help, please call Wor
     kstation"
             echo "          Services at x92396."
             echo
             exit 1
     }

     # Default to a black foreground with a white background.
     # Use the 9x15 and 9x15bold fonts. Connect to castor by default.
     #
     FG=black
     BG=white
     HOST=castor
     FONT=9x15
     BFONT=9x15bold
     COLS=80

     # Parse the command line arguments
     #
     while [ $# != 0 ];
     do
             case $1 in
                     -80)    COLS=80
                             FONT=spc12x24c
                             BFONT=spc12x24b
                             shift
                             ;;
                     -132)   COLS=132
                             FONT=9x15
                             BFONT=9x15b
                             shift
                             ;;
                     -fg)    shift
                             FG=$1
                             shift;;
                     -bg)    shift
                             BG=$1
                             shift;;
                     -fn)    shift
                             FONT=$1
                             shift;;
                     -fb)    shift
                             BFONT=$1
                             shift;;
                     -host)  shift
                             HOST=$1
                             shift;;
                     -help)  Usage;;
                     *)      Usage;;
             esac
     done

     xterm  -title "VAX" -sb -sl 1200 -geo ${COLS}x24 -fg ${FG} -bg ${BG}
      \
             -cr red -fn ${FONT} -fb ${BFONT} -xrm \
             'XTerm*VT100.translations:     #override \n\
             <Key>Insert:            string(\001) \n\
             Shift <Key>Up:          scroll-back(1,lines) \n\
             Shift <Key>Down:        scroll-forw(1,lines) \n\
             Shift <Key>Right:       string(0x1b) string("f") \n\
             Shift <Key>Left:        string(0x1b) string("b") \n\
             Shift <Key>Delete:      string(0x1b) string(0x08) \n\
             Shift <Key>Tab:         string(0x1b) string("*") \n\
             <Key>0x1000FF0D:        scroll-back(1,page) \n\
             <Key>0x1000FF0E:        scroll-forw(1,page) \n\
             <Key>0x1000FF09:        string(\010) \n\
             <Key>0x1000FF0A:        string(\005) \n\
             <Key>BackSpace:         string(0xff) \n\
             <Key>Select:            select-start() \n\
             <Key>0x1000FF02:        select-end(PRIMARY,CUT_BUFFER0) \n\
             Meta <Key>0x1000FF02:   select-end(CLIPBOARD) \n\
             <Key>0x1000FF04:        insert-selection(PRIMARY,CUT_BUFFER0
     ) \n\
             Meta <Key>0x1000FF04:   insert-selection(CLIPBOARD) \n\
             <Key>F1:                string(0x1b) string("OP") \n\
             <Key>F2:                string(0x1b) string("OQ") \n\
             <Key>F3:                string(0x1b) string("OR") \n\
             <Key>F4:                string(0x1b) string("OS") \n\
             <Key>F5:                string(0x1b) string("OA") \n\
             <Key>F11:               string(0x1b) string("[23~") \n\
             <Key>F12:               string(0x1b) string("[24~") \n\
             <Key>KP_0:              string(0x1b) string("Op") \n\
             <Key>KP_1:              string(0x1b) string("Oq") \n\
             <Key>KP_2:              string(0x1b) string("Or") \n\
             <Key>KP_3:              string(0x1b) string("Os") \n\
             <Key>KP_4:              string(0x1b) string("Ot") \n\
             <Key>KP_5:              string(0x1b) string("Ou") \n\
             <Key>KP_Divide:         string(0x1b) string("OP") \n\
             <Key>KP_Multiply:       string(0x1b) string("[29~") \n\
             <Key>KP_Enter:          string(0x1b) string("OM") \n\
             <Key>KP_Subtract:       string(0x1b) string("Om") \n\
             <Key>KP_Add:            string(0x1b) string("Ol") \n\
             <Key>KP_Decimal:        string(0x1b) string("On") \n\
             <Btn1Down>:             select-start() \n\
             <Btn1Motion>:           select-extend() \n\
             <Btn1Up>:               select-end(PRIMARY,CUT_BUFFER0) \n\
             Button1<Btn2Down>:      select-end(CLIPBOARD) \n\
             Button1<Btn2Up>:        ignore()' \
             -e telnet $HOST &

   Finally (for the moment) is a further modification of Robert Ess's
   script by Erik Ahlefeldt, <oahlefel@metz.une.edu.au>. From his readme
   file, for vmsterm:

     This script is for people who wish to connect from a Linux or Unix
     computer to a VMS computer using telnet and get a good VT100 or
     VT220 emulation. The key mappings have been specifically designed to
     emulate the VT terminal auxiliary numeric keypad, so that you can
     use VMS EDT and TPU editors, as well as the many VMS applications
     use keys PF1 to PF4. The script should work with any recent version
     of Xterm using a standard extended IBM PC keyboard or a Sun
     keyboard.

     About the keymappings. First the auxiliary numeric keypad. My prime
     objective with these mappings was to produce a setup that I could
     use with the EDT and TPU editors which make extensive use of the
     numeric keypad. The top row of keys PC numeric keypad (Num Lock,
     Divide, Multiply, Subtract) are where you find PF1, PF2, PF3, PF4 on
     a VT keyboard, so I have mapped them to PF1 thru PF4. The PC numeric
     keypad Add key (+) takes up the space of two keys which are Minus
     and Comma on the VT keyboard – I have mapped it to Comma (Delete
     Character in the EDT editor). I have then used the PC Pause key to
     map to VT key Minus (Delete Word in the EDT editor). The remaining
     keys on the auxiliary numeric keypad are the same for PC and VT.

     The six keys between the main and numeric keypads on the PC (Insert,
     Home, Page Up, Delete End, Page Down) are usually mapped to the VT
     keys by either position or by (approximate) function. As I rarely
     use these keys I have mapped them by function as follows: PC key
     Insert to VT Insert Here, PC Home to VT Find, PC Page Up to VT Prev,
     PC Delete to VT Remove, PC End to VT Select, PC Page Down to VT
     Next.

   Function keys.
          There are 12 function keys on the PC keyboard and 20 on the VT
          keyboard, so I map PC F1 thru F12 to VT F1 thru F12 (except for
          F1 thru F5 as noted below) and PC Shift F1 thru Shift F10 to VT
          F11 thru F20.

          The VT keys F1 thru F5 are local hardware function keys so there
          is nothing to emulate, however some PC to VT emulations in the
          past have mapped PF1 thru PF4 here, so I have done that too,
          even though they are already mapped on the auxiliary numeric
          keypad.

   Xterm functionality.
          You lose some xterm functions when you remap the keyboard,
          however this script implements a scroll back buffer of 1000
          lines which you scroll through using Shift and Up (a.k.a. Up
          Arrow or Cursor Up key) or Shift and Down.

   a summary of the keyboard mapping:

PC Key     maps to   VT Key.
------               ------
F1                   PF1
F2                   PF2
F3                   PF3
F4                   PF4
F5                   unused
F6                   F6
F7                   F7
F8                   F8
F9                   F9
F10                  F10
F11                  F11
F12                  F12
Shift F1             F11
Shift F2             F12
Shift F3             F13
Shift F4             F14
Shift F5             F15 (Help)
Shift F6             F16 (Do)
Shift F7             F17
Shift F8             F18
Shift F9             F19
Shift F10            F20
Shift F11            F11
Shift F12            F12
Print                Help (F15)
Cancel               Do   (F16)
Pause                Keypad Minus

Insert               Insert Here
Delete               Remove
Home                 Find
End                  Select
Prior                Prev
Next                 Next
BackSpace            BackSpace (sends DEL - ascii 127)

Num_Lock             PF1
KP_Divide            PF2
KP_Multiply          PF3
KP_Subtract          PF4
KP_Add               Keypad Comma
KP_Enter             Enter
KP_Decimal           Period
KP_0                 Keypad 0
KP_1                 Keypad 1
KP_2                 Keypad 2
KP_3                 Keypad 3
KP_4                 Keypad 4
KP_5                 Keypad 5
KP_6                 Keypad 6
KP_7                 Keypad 7
KP_8                 Keypad 8
KP_9                 Keypad 9
Up                   Up
Shift Up             Scroll Back
Down                 Down
Shift Down           Scroll Forward
Right                Right
Left                 Left

   and the script:

     #!/bin/sh
     #               vmsterm
     #               from an original script by Bob Ess
     #               key translations by Erik Ahlefeldt
     #
     #               Script file using Xterm and telnet to connect to a V
     MS host
     #               and give a decent vt220 emulation.
     #
     # Usage statement
     Usage(){
             echo
             echo " Usage  : vmsterm -options"
             echo
             echo " Options: -80   for 80 column terminal"
             echo "          -132  for 132 column terminal"
             echo "          -bg colorname"
             echo "          -fg colorname"
             echo "          -fn fontname"
             echo "          -fb bold fontname"
             echo "          -host [crusher.saltmine.com] [earth] [192.16
     8.7.7]"
             echo ""
             echo " Example: \"vmsterm -80 -fg white -bg black -fn 9x15 -
     fb 9x15b -host earth\""
             echo "          Starts a VMS session with an 80 column termi
     nal"
             echo "          with a black background, white foreground, a
      normal"
             echo "          font of 9x15 and a bold font of 9x15b, and c
     onnects"
             echo "          to the node 'earth'"
             echo ""
             echo " Example: \"vmsterm -host earth\""
             echo "          Starts a VMS session with default terminal s
     ettings "
             echo ""
             echo " Example: \"vmsterm -help\""
             echo "          Displays vmsterm options "
             echo
             exit 1
     }

     # Default to a black foreground with a white background.
     # Use the 9x15 and 9x15bold fonts. Connect to 192.168.3.3 by default
     .
     #
     FG=black
     BG=white
     HOST=192.168.3.3
     FONT=9x15
     BFONT=9x15bold
     COLS=80

     # Parse the command line arguments
     #
     while [ $# != 0 ];
     do
             case $1 in
                     -80)    COLS=80
                             FONT=spc12x24c
                             BFONT=spc12x24b
                             shift
                             ;;
                     -132)   COLS=132
                             FONT=9x15
                             BFONT=9x15b
                             shift
                             ;;
                     -fg)    shift
                             FG=$1
                             shift;;
                     -bg)    shift
                             BG=$1
                             shift;;
                     -fn)    shift
                             FONT=$1
                             shift;;
                     -fb)    shift
                             BFONT=$1
                             shift;;
                     -host)  shift
                             HOST=$1
                             shift;;
                     -help)  Usage;;
                     *)      Usage;;
             esac
     done

     xterm   -title "VMSTERM" -sb -sl 1000 -geo ${COLS}x24 -fg ${FG} -bg
     ${BG} \
             -cr blue -fn ${FONT} -fb ${BFONT} -xrm \
             "XTerm*vt100.translations: #override \n \
             ~Shift  <Key>F1:        string(0x1b)    string("OP") \n \
             ~Shift  <Key>F2:        string(0x1b)    string("OQ") \n \
             ~Shift  <Key>F3:        string(0x1b)    string("OR") \n \
             ~Shift  <Key>F4:        string(0x1b)    string("OS") \n \
             ~Shift  <Key>F5:        string("Break") \n \
             ~Shift  <Key>F6:        string(0x1b)    string("[17~") \n \
             ~Shift  <Key>F7:        string(0x1b)    string("[18~") \n \
             ~Shift  <Key>F8:        string(0x1b)    string("[19~") \n \
             ~Shift  <Key>F9:        string(0x1b)    string("[20~") \n \
             ~Shift  <Key>F10:       string(0x1b)    string("[21~") \n \
             ~Shift  <Key>F11:       string(0x1b)    string("[23~") \n \
             ~Shift  <Key>F12:       string(0x1b)    string("[24~") \n \
             Shift   <Key>F1:        string(0x1b)    string("[23~") \n \
             Shift   <Key>F2:        string(0x1b)    string("[24~") \n \
             Shift   <Key>F3:        string(0x1b)    string("[25~") \n \
             Shift   <Key>F4:        string(0x1b)    string("[26~") \n \
             Shift   <Key>F5:        string(0x1b)    string("[28~") \n \
             Shift   <Key>F6:        string(0x1b)    string("[29~") \n \
             Shift   <Key>F7:        string(0x1b)    string("[31~") \n \
             Shift   <Key>F8:        string(0x1b)    string("[32~") \n \
             Shift   <Key>F9:        string(0x1b)    string("[33~") \n \
             Shift   <Key>F10:       string(0x1b)    string("[34~") \n \
             Shift   <Key>F11:       string(0x1b)    string("[28~") \n \
             Shift   <Key>F12:       string(0x1b)    string("[29~") \n \
                     <Key>Print:     string(0x1b)    string("[28~") \n \
                     <Key>Cancel:    string(0x1b)    string("[29~") \n \
                     <Key>Pause:     string(0x1b)    string("Om") \n \
                     <Key>Insert:    string(0x1b)    string("[2~") \n \
                     <Key>Delete:    string(0x1b)    string("[3~") \n \
                     <Key>Home:      string(0x1b)    string("[1~") \n \
                     <Key>End:       string(0x1b)    string("[4~") \n \
                     <Key>Prior:     string(0x1b)    string("[5~") \n \
                     <Key>Next:      string(0x1b)    string("[6~") \n \
                     <Key>BackSpace: string(0x7f)    \n \
                     <Key>Num_Lock:  string(0x1b)    string("OP") \n \
                     <Key>KP_Divide: string(0x1b)    string("OQ") \n \
                     <Key>KP_Multiply: string(0x1b)  string("OR") \n \
                     <Key>KP_Subtract: string(0x1b)  string("OS") \n \
                     <Key>KP_Add:    string(0x1b)    string("Ol") \n \
                     <Key>KP_Enter:  string(0x1b)    string("OM") \n \
                     <Key>KP_Decimal: string(0x1b)   string("On") \n \
                     <Key>KP_0:      string(0x1b)    string("Op") \n \
                     <Key>KP_1:      string(0x1b)    string("Oq") \n \
                     <Key>KP_2:      string(0x1b)    string("Or") \n \
                     <Key>KP_3:      string(0x1b)    string("Os") \n \
                     <Key>KP_4:      string(0x1b)    string("Ot") \n \
                     <Key>KP_5:      string(0x1b)    string("Ou") \n \
                     <Key>KP_6:      string(0x1b)    string("Ov") \n \
                     <Key>KP_7:      string(0x1b)    string("Ow") \n \
                     <Key>KP_8:      string(0x1b)    string("Ox") \n \
                     <Key>KP_9:      string(0x1b)    string("Oy") \n \
             ~Shift  <Key>Up:        string(0x1b)    string("[A") \n \
             Shift   <Key>Up:        scroll-back(1,lines) \n \
             ~Shift  <Key>Down:      string(0x1b)    string("[B") \n \
             Shift   <Key>Down:      scroll-forw(1,lines) \n \
                     <Key>Right:     string(0x1b)    string("[C") \n \
                     <Key>Left:      string(0x1b)    string("[D")" \
             -e telnet $HOST

  How do I set the title?

   The control sequences for doing this are documented in ctlseqs.ms.

   The usual context for this question is setting the title according to
   the current working directory. People post answers to this periodically
   on the newsgroups. Here is one that I have seen, from Roy Wright
   <nobody@roystoy.dseg.ti.com>. In your /etc/profile after:

     if [ "$SHELL" = "/bin/pdksh" -o "$SHELL" = "/bin/ksh" ]; then
             PS1="! $ "
     elif [ "$SHELL" = "/bin/zsh" ]; then
             PS1="%m:%~%# "
     elif [ "$SHELL" = "/bin/ash" ]; then
             PS1="$ "
     else
             PS1='\u@\h:\w\$ '
     fi

   add:

     if [ "$TERM" = "xterm" ]; then
             PS1="\033]2;\u@\h:\w\007bash$ "
     fi

   The terminator "\007" is a problem area. XTerm historically uses this
   character, though it is non-ANSI. The "correct" character should be a
   "\233" string terminator, or "\033\\", which is the 7-bit equivalent.
   Modern xterm recognizes either (the "\007" or string terminator);
   waiting for the first of these.

   You may have resource or environment problems that prevent you from
   setting the title at all. Newer xterms (starting somewhere in X11R5)
   use the $LANG variable. If your locale is incorrectly installed, you
   will be unable to set the xterm's title. As noted by Mikhail Teterin
   <mi@rtfm.ziplink.net>: Make sure that the locale (LANG and/or LOCALE
   environment variable) is known to X Window System. Check
   ${X11ROOT}/lib/X11/locale.* for it. If it is not listed in either one
   of the files, find the nearest match and add an alias to it. Restart X
   if you have made changes.

   On a related note, some people want to know how to read the title from
   an xterm. This works for modern xterm and dtterm, but not for other
   variations:

     #!/bin/ksh
     # Echo the current X term title bar to standard output.
     # Written by Icarus Sparry <icarus@bath.ac.uk> 11 Apr 1997
     #
     exec </dev/tty
     old=$(stty -g)
     stty raw -echo min 0  time ${1-10}
     print "\033[21t\c" > /dev/tty
     IFS='' read -r a
     stty $old
     b=${a#???}
     print -R "${b%??}"

   But it is possible to avoid escape sequences altogether (from Hemant
   Shah <shah@typhoon.xnet.com>):

$ xprop -id $WINDOWID | grep WM_NAME
WM_NAME(STRING) = "this is my title"
current_title=$(xprop -id $WINDOWID | grep WM_NAME | cut -d= -f2)

   Here's another source of information: Xterm-Title HowTo

  How do I make the cursor blink?

   Standard xterm does not implement a blinking cursor. Some of the
   variations do: dtterm, GNOME Terminal, and modern xterm (from mid 1999,
   patch 107).

Frequent problems

     * Starting xterm, or not
          + Xterm does not run (no available pty's)
          + I need /etc/termcap
          + Why does $LD_LIBRARY_PATH get reset?
          + Why do the -e and -ls options not work together?
          + Why is my screen size not set?
          + Why are the menus tiny?
     * Font problems
          + My terminal doesn't show box characters
          + The bold font is ugly
          + I see little dots on the screen
          + My terminal doesn't display Cyrillic characters
          + I see boxes instead of characters in uxterm
          + I see question-marks instead of characters in uxterm
          + The first popup menu is very slow
     * Keyboard problems
          + Why can't I input 8-bit characters?
          + Why doesn't my delete key work?
          + Why did my delete key stop working?
          + Well, how can I set my delete key?
          + Why doesn't my keypad work?
          + How can my program distinguish control-I from tab?
          + Why can't I use the pageup/pagedown keys?
          + Why can't I use the home/end keys?
          + Why can't I use the cursor keys in (whatever) shell?
          + Alt-keys do not work in bash
     * Colors and other graphic rendition
          + My terminal doesn't recognize color
          + What $TERM should I use?
          + Reverse video is not reset
          + My colors changed in vim
          + Aren't bright colors the same as bold?
          + Can I set a color by its number?
          + I don't like that shade of blue
          + Why doesn't xterm support italics?
          + "grep --color" does not show the right output
          + That description of wrapping is odd, say more?
          + That color scheme is odd, say more?
     * Odd behavior
          + Why can't I select/paste in xterm?
          + Why can't I select/paste to/from other programs?
          + Why can't I select tab-characters in xterm?
          + FVWM does weird things when I try to resize xterm
          + Why doesn't the screen clear when running vi?
          + Why doesn't the screen clear when I type control/L?
          + Why is the cursor misplaced after running vi?
          + Why doesn't the scrollbar work?
          + Can I improve the scrollbars?
          + Can I improve the scrolling speed?
          + Why can't my program read the window title?
          + Why can't my program set the window size?
          + Why is the text in the wrong place?
     * Sample .Xdefaults Color-Settings for XTerm
     * What is this warning message?

  Starting xterm, or not

    XTerm does not run (no available pty's)

   Your copy of xterm may not have enough permissions to use existing
   pty's:
     * you may have to make xterm run setuid to root (though newer systems
       have wrappers that make this unnecessary).
     * the pty's permissions may be restrictive (that is ok, but you have
       to make xterm agree with it). Usually this is done by making the
       group ownership of the pty's "tty", and requiring that xterm run
       setgid to "tty". This is done rather than make xterm run setuid to
       root, since that presents problems with security.
     * newer systems (with Unix98 pty's) have a single entry under /dev
       which has to have the right permissions. For example:

# ls -l /dev/ptmx
crw-rw----    1 root     tty        5,   2 Aug 21 20:19 /dev/ptmx

   Perhaps your system does not have enough pty's, or (problems reported
   with newer Linux kernels supporting Unix98 pty's, beginning with RedHat
   6.0) the major device numbers of the pty's may have changed during a
   kernel upgrade. (This is described in /usr/src/linux/Documentation).

   See also the MAKEDEV script, which usually exists under /dev.

    I need /etc/termcap

   If you have a termcap version of xterm on a system with no termcap
   libraries, you may also be missing /etc/termcap.

   A workaround is to copy /usr/X11R6/lib/X11/etc/xterm.termcap to
   /etc/termcap.

   This is fixed another way starting with XFree86 3.3.1. If xterm cannot
   find the terminal description, it will accept that, though it will
   print a warning. If xterm does not find the termcap entry, it will not
   set the $TERMCAP variable.

    Why does $LD_LIBRARY_PATH get reset?

   If xterm is running setuid (which is needed on some systems which have
   no wrappers for opening pty's and updating utmp), newer systems
   automatically set or reset environment variables which are considered
   security problems. These include $PATH and $LD_LIBRARY_PATH, since they
   affect the choice of which programs are run if not specified via a full
   pathname.

   This means, for example, that if you attempt to run

xterm -e foo

   where foo is a program that uses shared libraries in /usr/local/lib,
   then the command will fail, because /usr/local/lib is not considered
   part of root's environment.

   Modern Unix systems (such as recent Solaris and HPUX versions) do not
   require you to run xterm setuid. Some will result in odd malfunctions
   if you do this.

    Why do the -e and -ls options not work together?

   XTerm has two useful options for controlling the shell that is run:

   -e
          tells xterm to execute a command using the remaining parameters
          after this option.

   -ls
          tells xterm to invoke a login shell, making it read your .login
          file, for instance.

   The two are not compatible. If you specify both, xterm uses -e, and if
   that fails for whatever reason will fall through to the -ls option. It
   cannot (in general) combine the two, since some shells permit this
   (e.g., bash), and others do not (e.g., tcsh).

    Why is my screen size not set?

   Well, it may be set, but not correctly. You may notice these symptoms:
     * When editing with vi, you cannot see the beginning of the file, or
     * Running

stty -a

       shows the rows and/or columns values as 0, or some other value
       (such as 65) which has nothing to do with the actual window size.

   XTerm knows how big the screen is (of course), and tries to tell your
   applications (e.g., by invoking ioctl's and sending SIGWINCH). But
   sometimes it cannot:
     * XTerm itself may have been built incorrectly (the #ifdef's that
       make the logic work are inactive).
     * You may be running xterm via a remote connection which refuses to
       pass that information. This can happen even on "modern" networks
       where the connection crosses domain boundaries.
     * You may be running su'd to another account. SIGWINCH is just
       another signal; signals do not propagate for security reasons.

   Most full-screen applications such as vi are designed to use the ioctl
   calls that return the screen size. When they fail, the applications use
   the size defined in the terminal's terminfo or termcap description.

   You may be able to use the resize program to issue the ioctl's that
   will notify your application of the actual screen size. This does not
   always work for the reasons just mentioned. Newer versions of stty let
   you specify the screen size, though it will not be updated if you
   resize the xterm window:

stty rows 24 columns 80

   Most full-screen applications also check if the $LINES and $COLUMNS
   variables are set, using those values to override the terminal
   description:

setenv LINES 24
setenv COLUMNS 80

   Why 65 lines? The standard xterm terminfo description specifies 65
   lines, perhaps because someone liked it that way. Real VT100's are 24
   lines. I once used (and wrote applications for) a Bitgraph terminal,
   which emulated VT100, but displayed 65 lines.

    Why are the menus tiny?

   Everything seems to work, except that the xterm menus (VT options,
   fonts, etc.) do not display properly; the menus pop up, but only with a
   tiny display area in which none of the options are visible (and only
   part of the menu title is visible).

   You have specified the geometry for xterm too high in the hierarchy,
   and that 24x80 (or whatever the -geometry parameter happens to be) is
   applying to the menus in pixels. This resource makes the geometry apply
   to the menus as well as the VT100 widget:

     XTerm*geometry: 80x24

   while this applies only to the VT100 widget (which is probably what you
   intended):

     XTerm.VT100.geometry: 80x24

   or better yet (to allow for the toolbar option, which uses a level of
   widget hierarchy):

     XTerm*VT100.geometry: 80x24

  Font problems

    My terminal doesn't show box characters

   XTerm displays the 7-bit ASCII and VT100 graphic characters (including
   box corners) using specially arranged fixed-pitch fonts. The first 32
   glyph positions (which would correspond to nonprinting control
   characters) are used to hold the VT100 graphic characters. Some fonts
   that otherwise look fine (such as courier) do not have glyphs defined
   for these positions. So they display as blanks. Use xfd to display the
   font.

   Modern xterm can form its own line-drawing characters (see patch 90,
   for example). It does not draw all of the graphic characters, only
   those that may be done with straight lines. But those are the most
   used, making most of the fixed-pitch fonts useful for xterm.

   You may also have a problem with the terminfo description. As
   distributed, the X11R6 terminfo for xterm does not have the acsc string
   defined, so most implementations of curses do not try to use the
   alternate character set.

   Finally, some people confuse the VT100 graphic characters with the
   VT220 support for DEC technical character set. These are distinct
   (7-bit) character sets. Xterm currently does not support this.

    The bold font is ugly

   XTerm lets you directly specify one bold font, which is assumed to
   correspond to the default font. Older versions of xterm make a fake
   bold font for the other choices via the fonts menu by drawing the
   characters offset by one pixel. I modified xterm to ask the font server
   for a bold font that corresponds to each font (other than the default
   one). Usually that works well. However, sometimes the font server gives
   a poor match. Xterm checks for differences in the alignment and size,
   but the font server may give incorrect information about the font size.
   The scaled bitmap font feature gives poor results for the smaller
   fonts. In your X server configuration file, that can be fixed by
   disabling the feature, e.g., by appending ":unscaled" to the path:

     FontPath        "/usr/lib/X11/fonts/100dpi/:unscaled"
     FontPath        "/usr/lib/X11/fonts/75dpi/:unscaled"
     FontPath        "/usr/lib/X11/fonts/misc/:unscaled"

   You can suppress xterm's overstriking for bold fonts using the
   alwaysBoldMode and related resources. However, rendering ugly bold
   fonts is a "feature" of the font server. In particular, the TrueType
   interface provides less ability to the client for determining if a
   particular font supports a bold form.

    I see little dots on the screen

   Well, I do. Perhaps you do not. It depends on the fonts you choose, and
   how you use them.

   Standard xterm has a "normal" font for which a bold font can be chosen,
   and several alternative fonts, useful for changing the font size. The
   alternative fonts do not have corresponding bold fonts. Xterm simulates
   bold fonts in this case by overstriking the character one pixel offset.
   That can make an bold character extend into the area that another
   character occupies. When erasing a bold character from the screen,
   xterm does not erase the extra pixel. This is corrected in modern
   xterm, subject to the available fonts (from late 1998, patch 85). For
   each font, it asks the font server for a corresponding bold font. Your
   font server may not have the bold font (or it may incorrectly report
   that it does). But it usually works.

    My terminal doesn't display Cyrillic characters

   Cyrillic encodings typically use characters in the range 128-159. For a
   VT220 (or any terminal that follows ISO 6429), those are treated as
   control characters. Still, some people want to use KOI8-R, etc. I
   modified xterm in patch 175 to add an option (-k8) and corresponding
   resource settings to allow them to customize their environment. Here is
   a sample script and resource file which I use for testing this
   configuration.

    I see boxes instead of characters in uxterm

   XTerm may show boxes instead of characters if the font that you have
   selected does not contain those characters. Normally you can fix most
   of that using the UTF-8 feature, with uxterm. However, your X resource
   settings may be the source of the problem.

   One pitfall to setting X resources is that they allow you to specify
   wildcards, e.g., the "*" character. When you give a wildcard, the X
   resource matches any number of levels in the widget hierarchy.

   XTerm has more than one widget matching "font" at different levels of
   the hierarchy. There are the popup menus, and there are the fonts used
   for uxterm. The latter is where an overbroad pattern can cause xterm to
   use a different font than you expect.

   Suppose your resource setting includes this pattern

     *VT100*font: fixed

   It could be interpreted as this:

     *VT100.font: fixed
     *VT100.utf8Fonts.font: fixed

   XTerm uses the utf8Fonts subresources to provide runtime-switchable
   fonts between IS0-8859-1 (Latin-1) and ISO-10646 (Unicode). Modifying
   the Unicode font to "fixed" will make most of the characters
   unavailable (i.e., shown as boxes). If instead your resource looks like

     *VT100.font: fixed

   it would be unambiguous, and not modify the utf8Fonts value.

    I see question-marks instead of characters in uxterm

   You may be seeing a question mark in a black diamond, like this:

     �

   That is called the Unicode replacement character. It is used when a
   program is told to display a character which is not in the Unicode
   system. The program replaces the illegal/invalid character with this
   symbol. That is different from boxes, which xterm displays when it has
   nothing in the current font for a valid Unicode character.

   Unicode's rules are oriented toward handling input in different
   encodings, and displaying the corresponding Unicode value. Although
   Unicode has rules and a definition for the valid characters, different
   programs may handle invalid input in different ways. This page gives an
   overview of how xterm may differ from other programs in that regard.

    The first popup menu is very slow

   Some users report that when starting xterm, it is very slow, that their
   computer's CPU time increases, etc.

   This is a longstanding bug in the X libraries. There is a workaround
   using a resource setting for xterm.

      Details

   XTerm uses the Athena (Xaw) widgets to display popup menus. In the
   normal case, those are initialized one-by-one as they are first used.
   If you have configured xterm to use its toolbar configuration, they are
   all initialized on startup. In the latter, performance problems are
   more noticeable.

   The Athena widgets XawInitializeWidgetSet function goes through several
   levels down to the X library _XlcAddUtf8LocaleConverters function to
   call create_tocs_conv and related functions to make a list of character
   sets from the locale, which is used in menus to get all possible fonts
   needed for a fontset.

   If your current locale uses UTF-8 encoding, this will read a long list
   of bitmap fonts—everything whose encoding might be useful for
   displaying the menus. For example, this list (from lcUTF8.c) which
   dates from around 2000 is the core of the problem:

     ISO10646-1, ISO8859-1, ISO8859-2, ISO8859-3, ISO8859-4, ISO8859-5,
     ISO8859-6, ISO8859-7, ISO8859-8, ISO8859-9, ISO8859-10, ISO8859-11,
     ISO8859-13, ISO8859-14, ISO8859-15, ISO8859-16, JISX0201.1976-0,
     TIS620-0, GB2312.1980-0, JISX0208.1983-0, JISX0208.1990-0,
     JISX0212.1990-0, KSC5601.1987-0, KOI8-R, KOI8-U, KOI8-C, TATAR-CYR,
     ARMSCII-8, IBM-CP1133, MULELAO-1, VISCII1.1-1, TCVN-5712,
     GEORGIAN-ACADEMY, GEORGIAN-PS, ISO8859-9E, MICROSOFT-CP1251,
     MICROSOFT-CP1255, MICROSOFT-CP1256, BIG5-0, BIG5-E0, BIG5-E1,
     ISO10646-1, ISO10646-1

   However, xterm is going to use only the characters shown in the popup
   menus. It is unlikely that you need Chinese fonts for that.

      Solution

   XTerm's menuLocale resource can be set to an explicit value, e.g., "C"
   to override the current locale as seen by this initialization debacle.

      Limitations

   The workaround does not prevent some hacker from "improving" the X
   libraries still further.

  Keyboard problems

    Why can't I input 8-bit characters?

   You must have the eightBitInput resource set to do this.

    Why doesn't my delete key work?

   This seems to have begun as a problem with the older XFree86 release
   (3.1.2). I have picked up pieces of the story (xterm and the keyboard
   work as designed under XFree86 3.2 and up).

   The underlying problem is that we've accumulated three things that are
   being equated as "Delete":

ASCII BS (backspace, code 8)
ASCII DEL (delete. code 127)
VT220 "remove" aka "delete" (ESC [ 3 ~)

   You are probably talking about the backarrow key (on my keyboard, at
   the upper right of the QWERTY block), or the key labeled delete which
   is on the 6-key "editing keypad". Since xterm is emulating a
   VT100/VT220, the backarrow key should generate a 127 (often displayed
   as ^?). You would use a control/H to obtain a backspace on a real
   VT220.

   The reason why BS and DEL are of special interest is that on Unix, the
   stty command and the underlying termios/termio system calls allow only
   single-byte codes to be assigned to special functions such as erase.
   For instance, you could see something like this on your terminal:

$ stty -a
speed 38400 baud; rows 40; columns 80; line = 0;
intr = ^C; quit = ^\; erase = ^H; kill = ^U; eof = ^D; eol = <undef>;
eol2 = <undef>; swtch = <undef>; start = <undef>; stop = <undef>; susp = <undef>
;
rprnt = ^R; werase = ^W; lnext = ^V; flush = ^O; min = 1; time = 0;
-parenb -parodd cs8 -hupcl -cstopb cread -clocal -crtscts
-ignbrk brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr -icrnl ixon -ixoff
-iuclc -ixany -imaxbel -iutf8
-opost -olcuc -ocrnl -onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff
0
isig -icanon -iexten -echo -echoe -echok -echonl -noflsh -xcase -tostop -echoprt
-echoctl -echoke

   Tastes differ. On Unix, people expect the backarrow key to generate a
   backspace (or not). As I understand it, at one point, XFree86 picked up
   the sense of the erase character during initialization, so that xterm
   would in effect use the same erase character as the console. The
   current scheme (X11R6) uses keyboard mapping tables that are
   independent of the environment.

   Modern xterm (since patch #83 in 1998) provides a resource toggle
   backarrowKey (and an escape sequence from VT320) that changes this key
   between the two styles (backspace or delete).

   With modern xterm patch 95 (also in the stable version as "88c"), you
   may have an xterm which can automatically initialize the backarrow key
   to backspace or delete depending on the pseudo terminal's sense, or
   based on the termcap setting of kbs (backspace key). This feature is
   controlled by the resource setting ptyInitialErase.

    Why did my delete key stop working?

   Well, something changed. You have to determine what did.

   This may be because an upgrade introduced different X resource
   settings, or because you are using the newer xterm with the
   ptyInitialErase resource (or perhaps both). Use

appres XTerm

   to see the X resources that you are using, in particular the
   translation (or Translation) resource for the vt100 widget.

   One unexpected scenario came out of hiding when I was implementing the
   ptyInitialErase resource. When xterm is (by default) built to support
   this, it sets the pty's erase character to match the termcap entry.
   Xterm also sets the $TERMCAP environment variable to match. So
   everything is consistent, and everything defined. The stty erase
   character is either backspace (^H) or delete (^?).

   The problem arises because there are two things called "delete", which
   were not well-defined: ASCII delete (127) and the PC-style adaptation
   of VT220 remove assigned to the key Delete.

   However, the screen program prefers to make the termcap delete (kD) an
   <escape>[3~, which corresponds to the VT220 remove key. If $TERMCAP is
   set when starting screen, it will translate stty's erase character into
   the <escape>[3~, making most curses and termcap applications work. But
   stty still has the original erase character. So low-level applications
   which check stty will not work. I found that unsetting $TERMCAP before
   running would work, but this was not a good solution. Someone pointed
   out (see patch 129), that the problem really was because termcap kD
   should delete the character at the current position. So it cannot be
   the same as stty erase.

   As a matter of fact, stty erase has to be a single character, so
   <escape>[3~ would not work anyway.

    Well, how can I set my delete key?

   When people first started asking this question in 1995-1996, it
   appeared in the context of making Netscape work. Netscape's use of the
   delete key running in X did not match user's expectations when compared
   to that other platform. They were commonly advised to use xmodmap,
   e.g.,

keysym BackSpace = Delete

   or

keycode 22 = 0xff08

   Either way is a bad technical solution – it works for some people but
   not others (on my keyboard at work, keycode 22 is the numeric keypad
   '9').

   Alternatively, you can set resources. This works reasonably well for
   environments where you have different versions of xterm, e.g.,

     XTerm*VT100.translations: #override \n\
             <Key>Delete: string(0x7f)

   I do not do that either, because it is not flexible. Not all programs
   use the same sense of stty erase; some use termcap or terminfo, and
   some are hardcoded. So I prefer to be able to switch the xterm's
   keyboard at runtime. You cannot do that with resources. (Or not really
   – xterm has a keymap() action which could support this if you provided
   a rather complex resource settings, but the X library support for that
   is broken in X11R6). Instead, I have added to xterm a set of resources
   (and popup menu entries) to allow simple switching between the
   different styles of keyboard, in particular for the backspace/delete
   issues. See the manual page for backarrowKey backarrowKeyIsErase and
   deleteIsDEL as well as sunKeyboard.

    Why doesn't my keypad work?

   A few people have commented that the keypad does not work properly.
   Aside from bugs (I have fixed a few), the most common problem seems to
   be misconception.

   Here's a picture of the VT100 numeric keypad:

+-----+-----+-----+-----+
| PF1 | PF2 | PF3 | PF4 |
+-----+-----+-----+-----+
|  7  |  8  |  9  |  -  |
+-----+-----+-----+-----+
|  4  |  5  |  6  |  ,  |
+-----+-----+-----+-----+
|  1  |  2  |  3  |     |
+-----+-----+-----+ ENT +
|     0     |  .  |     |
+-----+-----+-----+-----+

   and the similar Sun and PC keypads:

+-----+-----+-----+-----+
| NUM |  /  |  *  |  -  |
+-----+-----+-----+-----+
|  7  |  8  |  9  |     |
+-----+-----+-----+  +  +
|  4  |  5  |  6  |     |
+-----+-----+-----+-----+
|  1  |  2  |  3  |     |
+-----+-----+-----+ ENT +
|     0     |  .  |     |
+-----+-----+-----+-----+

   Working in X11, the NUM (NumLock) key has better uses than an alias for
   PF1 (and is sometimes reserved). I use the F1 through F4 on the
   keyboard to implement PF1 through PF4, alias the keypad "+" to "," and
   use the existing "-" key.

   VT220 emulation uses the VT100 numeric keypad as well as a 6-key
   editing keypad. Here's a picture of the VT220 editing keypad:

+--------+--------+--------+
| Find   | Insert | Remove |
+--------+--------+--------+
| Select | Prev   | Next   |
+--------+--------+--------+

   and the similar Sun and PC keypads:

+--------+--------+--------+
| Insert | Home   | PageUp |
+--------+--------+--------+
| Delete | End    | PageDn |
+--------+--------+--------+

   I chose to use keys that are mnemonic rather than in the "same"
   positions, though some emulators (e.g., Tera Term) use the same
   positions:

+--------+--------+--------+
| Insert | Find   | Prev   |
+--------+--------+--------+
| Remove | Select | Next   |
+--------+--------+--------+

   I test the keyboard (for VT52/VT100/VT220) using vttest. If you find
   (or think that you have found) a problem with the keyboard handling of
   xterm, please test it with vttest first.

   Other arrangements of the keyboard are possible of course. If you
   prefer to use the top row of the numeric keypad as PF1 through PF4, you
   should do this using xterm's X resources.

   In 2014, I noticed a comment, which relates to the PF1-PF4 assignment,
   but also to the use of function-key modifiers.
   Because that is a digression, I have expanded it in a separate page.

    How can my program distinguish control-I from tab?

   Your program can use xterm's modifyOtherKeys feature, e.g., using a
   control sequence such as

\033 [ > 4 ; 2 m

   to temporarily switch into a mode where shift, alt, control and meta
   modifiers applied to a key tell xterm to send an escape sequence which
   encodes all of that information. The tab key would send a tab, but
   control-i would send

\033 [ 2 7 ; 5 ; 1 0 5 ~

   while control-shift-i would send

\033 [ 2 7 ; 6 ; 7 3 ~

   Your program should turn that off when it is not needed; it is a real
   nuisance when you cannot type control-characters as they were meant to
   be used:

\033 [ > 4 m

   In 2019, Bram Moolenaar asked for more details about modifying other
   keys; I have expanded that in a separate page.

    Why can't I use the pageup/pagedown keys?

   Some vendors, e.g,. Sun, added key translations which make the pageup
   and pagedown keys talk to the xterm's scrollbar instead of your
   application. They did the same thing for the home and end keys, thereby
   obscuring a bug in xterm.

   You can override this by specifying your own translations in your
   resource file. The issue was first noted with Solaris 2.5, with the
   file given in two locations:

/usr/lib/X11/app-defaults/XTerm
/usr/openwin/lib/app-defaults

   using a symbolic link to relate the two. Later releases of Solaris,
   e.g., 8-10 omitted the former location.
   Solaris 11 provides modern xterm (patch #271), and does not have this
   problem.

   As of February 2014, I am able to verify that AIX and HPUX have updated
   to modern xterm, e.g.,
     * patch #180 on HPUX 11.31,
     * patch #222 on AIX 6.1 and 7.1,

   Older AIX and HPUX releases distributed the X Consortium (1994)
   app-defaults file.

     In updating this question in February 2014, I noticed that IBM added
     their copyright notice in AIX's copy of the app-defaults file in

/usr/lpp/X11/lib/X11/app-defaults

     There were no other changes to the file. Someone at IBM blundered.
     In patch #252, I ensured that my copyright notice is on those files
     (I am the sole author, and can do that).

   Use the translations in the system's app-defaults file as a guide. The
   relevant section of the app-default file looks like

     *VT100.translations:    #override \
             @Num_Lock<Key>KP_0: string(0)\n\
             @Num_Lock<Key>KP_1: string(1)\n\
             @Num_Lock<Key>KP_2: string(2)\n\
             @Num_Lock<Key>KP_3: string(3)\n\
             @Num_Lock<Key>KP_4: string(4)\n\
             @Num_Lock<Key>KP_5: string(5)\n\
             @Num_Lock<Key>KP_6: string(6)\n\
             @Num_Lock<Key>KP_7: string(7)\n\
             @Num_Lock<Key>KP_8: string(8)\n\
             @Num_Lock<Key>KP_9: string(9)\n\
             @Num_Lock<Key>KP_Add: string(+)\n\
             @Num_Lock<Key>KP_Decimal: string(.)\n\
             @Num_Lock<Key>KP_Divide: string(/)\n\
             @Num_Lock<Key>KP_Enter: string(\015)\n\
             @Num_Lock<Key>KP_Equal: string(=)\n\
             @Num_Lock<Key>KP_Multiply: string(*)\n\
             @Num_Lock<Key>KP_Subtract: string(-)\n\
             <Key>Prior:scroll-back(1,page)\n\
             <Key>Next:scroll-forw(1,page)\n\
             <Key>F16: start-extend() select-end(PRIMARY, CUT_BUFFER0, CL
     IPBOARD) \n\
             <Key>F18: insert-selection(PRIMARY, CLIPBOARD) \n\
             <Key>F27: scroll-back(100,page) \n\
             <Key>R13: scroll-forw(100,page) \n\
             <Key>Home: scroll-back(100,page) \n\
             <Key>End: scroll-forw(100,page) \n

   For example, a more-specific pattern for the resource name lets you
   override:

     XTerm*VT100.translations:       #override \n\
             ~Shift<Key>Home:  string(\033[1~)\n\
             ~Shift<Key>End:   string(\033[4~)\n\
             ~Shift<Key>Prior: string(\033[5~)\n\
             ~Shift<Key>Next:  string(\033[6~)\n\
             Shift<Key>Prior:  scroll-back(1,page) \n\
             Shift<Key>Next:   scroll-forw(1,page) \n\
             Shift<Key>Home:   scroll-back(100,page) \n\
             Shift<Key>End:    scroll-forw(100,page) \n

   makes the home/end and pageup/pagedown keys usable by your editor,
   while leaving their shifted equivalents available for the scrollbar.

    Why can't I use the home/end keys?

   This is a long story, unless you are referring to X Consortium xterm.
   That program is simply broken in this respect.

   At the beginning, when the home/end keys were fixed for modern xterm
   (in early 1996), there was some discussion regarding what the escape
   sequences should be for those keys (for the 6-key editing keypad).
   Those were chosen as "PC-style" codes (like SCO "ansi"), i.e.,

ESC [ H
ESC [ F

   for normal mode, and

ESC O H
ESC O F

   for cursor application mode.

   That style of coding fit easily into the existing logic of xterm. It
   was not my change, and (because xterm should be based upon standards),
   I did question this, and asked the opinion of the person who was at
   that time developing rxvt. He had chosen a layout based on DEC's VT220
   terminals, though the key labels on the typical PC keyboard did not
   match. At that point, neither of us knew enough to make a good case for
   this.

   Somewhat later I could see that xterm had a number of undocumented
   extensions to support the VT220-style (pre-ISO 2022) character sets. I
   decided to complete the functionality by making xterm a VT220 emulator.
   This would require that it provide the same escape sequences for the
   editing and numeric keypads. I could not simply change the escape
   sequences from "PC-style" to "VT220-style", since a number of users
   "knew" that the keypad "ought to" send home, end, cursor keys, etc.,
   because they had labels indicating that use. To retain compatibility
   (but allow easy reconfiguration to make a VT220 emulator), I added
   popup-menu items to switch between the modes. With minor refinements,
   this was the approach for about two years, culminating with the
   "stable" patch #88, which is essentially the version distributed with
   XFree86 3.3.x.

   NOTE:
          the terminfo distributed with xterm patch #88 is incorrect: the
          escape sequences given for home/end keys are the VT220-style,
          rather than the default PC-style. Too accustomed to switching
          modes on the fly, I overlooked a line in my .Xdefaults file:

     *sunKeyboard: true

          Downstream packagers (when they noticed this) accommodated the
          bug by modifying the VT100 translations resource which is not a
          good technical solution since it interferes with the users'
          ability to modify that resource. For example, Red Hat bug
          #100695 quoted a suggested patch which shows that the package
          had overridden the xterm behavior for shifted function keys. See
          this for more discussion.

   But xterm continues to evolve past the stable patch #88. The keyboard
   support was still unsatisfactory for two reasons:
     * some users wanted to be able to use applications that detected
       whether the control key was pressed (e.g., control/F1).
     * the compromises made for xkb with X11R6 interfered with xterm's use
       of the NumLock key for the numeric keypad.

   The former could be addressed by expanding the escape sequences sent by
   the PC-style function keys, while the latter was a VT100/VT220 design
   issue. I decided to redesign function-key support to separate the two
   styles of function keys better, but leaving the choice still controlled
   by the sunKeyboard resource. Partway through that, I was asked to do
   similar cleanup and redesign of the backspace and delete key handling,
   e.g., the ptyInitialErase resource. Because it is a redesign, I chose
   to not make the keyboard differences between the old and new xterms
   completely compatible. If you were to run both on the same system, one
   or the other would have some problems with the editing keypad or the
   backspace/delete keys which would be addressed by the popup-menu
   selections.

   For example, at this time (2001/9/4):
     * Debian stable is xterm-88c, which should be identical to the
       XFree86 3.3.6 version, but is not (there are some label differences
       in the resource-file, but nothing interesting relative to home/end
       keys). And of course, Debian changes the terminfo kbs from ^H to
       ^?. As noted, the terminfo I wrote for XFree86 3.3.x has an error.
       Setting

     *sunKeyboard: true
       in the app-defaults file fixes the problem with xterm-88, which was
       that I documented in the terminfo the behavior with that resource
       set. Similarly, setting

     *backarrowKey: false
       is one way to address Debian's change to kbs.
     * Debian unstable is xterm-149. Other than omitting the color
       resources from the app-defaults file, I see that it sets

     *backarrowKeyIsErase: true
       which would not affect the home/end keys. (The color resources are
       redundant, so that is not a problem either).

   Here is a resource file which I tested with xterm-88c, xterm-149 and
   xterm-158, using $TERM set to xterm-debian:

     ! $Id: xterm.faq.html,v 1.169 2012/02/05 11:58:56 tom Exp $
     ! Settings to make xterm-88c work as expected for Debian.
     !
     ! Patch #88 was the basis for XFree86 3.3.1 xterm.  There were a few
      additions
     ! through patch 88c, to incorporate the ptyInitialErase resource.  D
     ebian uses
     ! the VT220-style keyboard, which at #88 was the xterm-xfree86 termi
     nfo entry,
     ! with one change: kbs changed from ^H to ^?.
     !
     ! After patch 88, I started work on keyboard changes.  The result wa
     s that the
     ! xterm-xfree86 terminfo entry was set to the PC-style keyboard, and
      I added
     ! xterm-vt220, which corresponded mostly to the older (patch-88) ver
     sion of the
     ! xterm-xfree86 terminfo entry.

     ! The terminfo with patch #88 assumed sunKeyboard was set (actually
     a bug, but
     ! also assumed in Debian).
     !
     ! A different problem (addressed after patch #88) is that if you wan
     ted to use
     ! a VT100/VT220-style numeric keypad's escape sequences, you had to
     have
     ! NumLock set.  Otherwise, in keypad application mode, the keys woul
     d transmit
     ! only the PC-style escape sequences corresponding to the key labels
     , e.g., the
     ! page-up string rather than the escape sequence for keypad-9.
     XTerm*sunKeyboard: true

     ! These settings overlap to some extent (backarrowKeys says to send
     a 127 for
     ! the "backspace" key, and ptyInitialErase says to use the pty's ini
     tial sense
     ! of the erase character, which is reported to be the same on Linux)
     .
     XTerm*backarrowKey: false
     XTerm*ptyInitialErase: true

    Why can't I use the cursor keys in (whatever) shell?

   VTxxx (VT100 and up) terminals may send different escape sequences for
   the cursor (arrow) keys depending on how they are set up. The choices
   are referred to as the normal and application modes. Initially, the
   terminal is in normal mode.

   VTxxx terminals are usually set up so that full-screen applications
   will use the cursor application mode strings. This is good for
   full-screen applications, including legacy applications which may have
   hard-coded behavior, but bad for interactive shells (e.g., ksh, tcsh,
   bash) which use arrow keys to scroll through a history of command
   strings.

   To see the difference between normal/application modes, consider this
   example:
     * In normal (non-application) mode, the terminal transmits a
       down-arrow as \E[C, which happens to echo as a down-arrow.
     * In application mode the terminal transmits \EOC, which echoes as C.
       That is because the \EO is the SS3 control, which says to use the
       character from the G3 character set for the next cell.

   Since termcaps and terminfo descriptions are written for full-screen
   applications, shells and similar programs often rely on built-in tables
   of escape sequences which they use instead. Defining keys in terms of
   the termcap/terminfo entry (e.g., by capturing the string sent by
   tputs) is apt to confuse the shell.

   Depending on the terminal type, the keypad(s) on the keyboard may
   switch modes along with the cursor keys, or have their own independent
   modes. The control sequences for these are independent of the ones used
   for cursor-addressing, but are grouped together, e.g., as the terminfo
   smkx and rmkx capabilities. Terminfo entries are written assuming that
   the application has initialized the terminal using the smkx string
   before it is able to match the codes given for the cursor or keypad
   keys.

    Alt-keys do not work in bash

   See Alt-keys do not work in bash.

  Colors and other graphic rendition

    My terminal doesn't recognize color

   First, ensure that you have set up xterm to render color. Modern xterm
   renders color only if you have set resources to do this; the default
   behavior is monochrome to maintain compatibility with older
   applications. The manual page describes these resources. I set them in
   my .Xdefaults file.

   Even if you set the resources properly, there may be another
   application running which prevents xterm from allocating the colors you
   have specified. But you should see a warning message for this.

   Check the terminal description, to see if it is installed properly,
   e.g., for ncurses, which uses terminfo.

   Finally, some applications (that do not interface properly with
   terminfo or termcap) may need the environment variable $COLORTERM to be
   set.

    What $TERM should I use?

   XTerm provides in its sources both terminfo and termcap files. They are
   designed to allow scripting to override the most common choices, e.g.,
   the backspace key.

   The xterm-color value for $TERM is a bad choice for modern xterm
   because it is commonly used for a terminfo entry which happens to not
   support bce. Complicating matters, FreeBSD (after dithering for a few
   years on the matter) introduced a bastardized version which implies the
   opposite sense of bce, (because it uses SGR 39 and 49), but does not
   set it. After lengthy discussion, FreeBSD began using the terminal
   descriptions which I've written.

   The most recent XFree86 version's terminal description corresponds to
   xterm-xfree86 (also distributed with ncurses). I have continued to make
   changes; the most recent version is simply named xterm-new (also
   distributed with ncurses).

   The term "bce" stands for "back color erase". Terminals such as modern
   xterm and rxvt implement back color erase, others such as dtterm do
   not. (Roughly half of the emulators that I know about implement bce).
   When an application clears the screen, a terminal that implements back
   color erase will retain the last-set background color. A terminal that
   does not implement back color erase will reset the background color to
   the default or initial colors. Applications that paint most of the
   screen in a single color are more efficient on terminals that support
   back color erase. Inevitably, there are tradeoffs and issues with
   standardization of the feature as noted in the ncurses FAQ.
   Unsurprisingly, ncurses supports xterm's behavior.

   Curses libraries that support color know about bce and do the right
   thing – provided that you tell them what the terminal does. That is the
   whole point of setting $TERM. The "xterm-color" description distributed
   with ncurses does not list bce, because it was applied originally to a
   terminal type which does not implement back color erase. It will "work"
   for modern xterm, though less efficient. Some other applications such
   as the slang library have hardcoded support for terminals that
   implement back color erase. Given the "xterm-color" description, those
   will be efficient – and fortuitously work. However, slang (through
   version 1.4.0) did not work properly for the terminals that xterm-color
   was designed for. See this page for an example of (n)curses and slang
   running on dtterm. That bug in slang is reported to be fixed for
   succeeding versions, though your application may require changes to use
   this fix. (The demo which comes with slang to illustrate the use of bce
   does not work properly, for instance).

   The xterm-color value for $TERM is also (for the same reason) a bad
   choice for rxvt, but "works" due to the large number of hard-coded
   applications that override this.

   Some people recommend using xtermc. That is installed on Solaris.
   However, it does not match any xterm in current use. (Apparently it was
   written for an obsolete version on Unixware). The colors work, true,
   but the mouse will not, nor will the function keys.

    Reverse video is not reset

   When running less or other programs that do highlighting, you see the
   highlighting not turned off properly.

   This may be due to incompatible terminal descriptions for xterm. With
   XFree86 3.2, I modified the terminal description for XFree86 xterm to
   use the VT220 (aka ISO 6429) controls that allow an application to turn
   off highlighting (or bold, underline) without modifying the other
   attributes. The X Consortium xterm does not recognize these controls.

   If, for example, you are running an older xterm and rlogin to a system
   where the newer xterm has been installed, you will have this problem,
   because both programs default to $TERM set to xterm. The solution for
   mixed systems is to install the newer terminal description as as a
   different name (e.g., xterm-color) and set the termName resource
   accordingly in the app-defaults file for the system which has the newer
   xterm.

   However – see above.

    My colors changed in vim

   Some vim users may notice their colors change after updating to patch
   238. Before, some text would display in a dark color using a bold font.
   Now, it displays in a bright color and normal font.

   This is not a bug, but the result of a feature tcap-query which was
   added for vim in 2000. Several vim users requested that it be enabled
   by default in the configure script. It allows vim to ask what
   characters the different function keys actually send, eliminating the
   chance that the termcap does not match.

   Vim also asks how many colors the terminal supports. Since patch 148,
   xterm has responded with the number of distinct colors that it can
   display. By default, that is 16 (8 ANSI colors with bright counterparts
   for displaying PC-style "bold" text).

   The interpretation of this depends on the application: termcaps do not
   tell how to display more than 8 colors. But vim understands how to tell
   xterm to display using 16 colors. It makes a difference when displaying
   bright colors. Vim has a table of 16 color names ("dos-colors"), which
   one can use to define parts of the color scheme. If the terminal
   supports only 8 colors (colors 0-7), vim uses the bold attribute to
   simulate colors 8-15.

   Changing the color scheme to use bold where it is wanted will make the
   colors work as before – and work consistently with other terminals.

    Aren't bright colors the same as bold?

   No.

   Actually, "bold" happens to be whatever the terminal shows when it is
   sent the control-string that says "show bold".

   The standard (ANSI aka ISO-6429 or ECMA-48) says no more than that.
   ANSI specified eight (8) colors. In fact, ANSI did not specify the
   appearance. That is an implementation detail.

   XTerm can be configured to use colors 8-15 for displaying bold text. Or
   it can be configured to use those colors as part of a 16-color scheme
   (a feature of aixterm). They use different control strings. When xterm
   is configured to use the 16-color scheme, it displays bold text by
   relying on the font to show "bold" (usually thicker characters).

   By default, colors 8-15 are brighter versions of colors 0-7 (with some
   special handling for blue). But again, xterm is configurable and you
   can use anything that you like for the numbered colors.

    Can I set a color by its number?

   Well, yes: you can set a color in several ways:
     * using the color name
     * using an RGB value
     * selecting an index from the color palette

   That last (an index) is what some people think of as the color number.
   The short answer is that you can find on the web tables of colors and
   match them up to the “color number”. But the number itself has no
   meaning.

   In my reply to tput setaf color table? How to determine color codes?, I
   noted

     You may find this question/answer helpful as well: RGB values of the
     colors in the Ansi extended colors index (17-255)

   although both question and answer raise additional questions. This FAQ
   is the logical place to answer those questions.

   Presumably you are reading this to better understand how xterm works.
   But you may be interested in the way in which other terminals emulate
   xterm. If so, this explanation may help as well.

   The long answer is that the correct mapping depends on the terminal —
   other terminals do not necessarily match xterm.

   From a shell script, you might use tput with a parameter to an escape
   sequence referred to as setaf in the terminal description. tput
   attaches no particular meaning to the number. That actually depends
   upon the particular terminal emulator.

   A while back, ANSI defined codes for 8 colors, and there were two
   schemes for numbering those. The two are seen in some terminal
   descriptions as the pairs setf/setb or setaf/setab. Since the latter
   has the connotation of "ANSI colors", you will see that used more
   often. The former (setf/setb) switched the order for red/blue as noted
   in Why are red/blue interchanged?, but in either case, the scheme was
   established for just numbering the colors. There is no predefined
   relationship between those numbers and RGB content.

   For specific terminal emulators, there are predefined color palettes
   which can be enumerated easily enough — and can be programmed using
   these escape sequences. There are no relevant standards, and you will
   see differences between terminal emulators, as noted in I don't like
   that shade of blue.

   However, convention is often confused with standards. Because xterm has
   been around a while, it is regarded as a standard by some.

   XTerm had color support before I began working on it at the end of
   1995. Some of this was mentioned in XFree86's changelog:

XFree86 3.1.2Be (10 January 1996)
203. Major xterm cleanup (including prototyping), and fixes to the colour
     code (Thomas E. Dickey).
XFree86 3.1.2a (23 September 1995)
 14. Colour support for xterm (David Wexelblat).
 13. Fix usage of $LINES and $COLUMNS by xterm on SVR4 (David Wexelblat).

   and some was not:
     * The “dynamic colors” feature came from a patch written by Erik
       Fortune (at SGI). Someone applied this to the XFree86 sources
       (probably early 1995).
       Since X11R4, xterm had colors for foreground and background in the
       VT100 and Tek4014 widgets, as well as cursor- and mouse-colors
       which could be set via resources. But those were static. The
       dynamic colors feature allowed those colors to be set via escape
       sequences.
     * “Colour support” was a set of changes for ANSI color. It might have
       been based on a patch (said to be of unknown authorship) for X11R5
       xterm incorporated into a program called color_xterm. Raymond's
       comment in terminfo.src implies that this program was distributed
       earlier; however the copy of color_xterm-alpha4 which I have at
       hand has file modification dates starting in December 1995.
       Wexelblat's commit is an earlier non-patch use of the feature for
       xterm.
       Both were probably due to Tom Weinstein (also at SGI) in 1992,
       which you can find in the historic Linux archive. The README.color
       file in this earlier color_xterm says

2) Added ISO 6429 support for color text.  You can set the foreground
   and background color for text using SGR.  For example, to make the
   foreground red, you do:  "^[[31m".  The values from 30 to 37 set
   foreground, those from 40 to 47 set background.  The default colors
   are:
        0) black   1) red   2) green  3) yellow  4) blue  5) magenta
        6) cyan    7) white

   These are settable with the resources "color0" to "color1"

       Aside from README.color, there was no documentation. The terminal
       description was unmodified.

   Thus, from the start there were two types of color support in xterm.
   ANSI colors treats the available colors as an array (its palette) which
   can be programmed, while dynamic colors applies a single color to a
   feature.

   There have been some changes since the color_xterm in 1992:

     Resource   1992    1995       2016
     color0   Black   black    black
     color1   Red     red3     red3
     color2   Green   green3   green3
     color3   Yellow  yellow3  yellow3
     color4   Blue    blue3    blue2
     color5   Magenta magenta3 magenta3
     color6   Cyan    cyan3    cyan3
     color7   White   gray90   gray90
     color8           gray30   gray50
     color9           red      red
     color10          green    green
     color11          yellow   yellow
     color12          blue     rgb:5c/5c/ff
     color13          magenta  magenta
     color14          cyan     cyan
     color15          white    white
     colorUL          yellow   foreground
     colorBD          white    foreground
     colorRV                   foreground
     colorIT                   foreground

   In development of xterm over the past 20 years, we
     * incorporated ANSI (8) colors,
     * adapted the aixterm feature (16) colors,
     * added extensions for 88- and 256-colors.

   Much of that has been adopted by other developers for different
   terminal emulators. That is summarized in Why not make "xterm" equated
   to "xterm-256color"?.

   As hinted by the table, the 16-color extension was partly implemented
   in xterm by late 1995, using the scheme of Linux console: bold fonts
   are shown as brighter equivalents of the ANSI 8 colors. Unlike the
   Linux console, xterm can use bold fonts and (aside from providing
   similar appearance to the Linux console for programs such as dialog)
   there was no reason to pretend that bold and bright were synonymous.

   The colorUL and colorBD features are part of this discussion because I
   incorporated those into the indexing scheme for colors. More on that
   later.

   First, deal with the 256- and 88-color extensions.

   The reason for 256 colors is that the index would fit in a byte.
   Larason's scheme was simple enough:
     * the existing 16 colors
     * a color cube (6x6x6 is 216, which is the largest cube no larger
       than 256).
     * a grayscale "ramp", using the remaining 24 entries.

   The xterm source-code includes scripts for demonstrating the colors,
   e.g., using the same escape sequences that tput would use:
     * patch #94 (1999/03/27) added 8colors.sh, 16colors.sh
     * patch #111 (1999/07/10) added 256colors.pl and 256colors2.pl
     * patch #115 (1999/07/18) added 88colors.pl and 88colors2.pl

   I added the scripts in patch #94 because of some user comments that
   there were scripts of that sort available, that there were some
   deficiencies in those, and and it would be nice to have some good
   examples in xterm's source. Coincidentally, that gave Todd Larason and
   Stephen P Wall a starting point for the changes to support 256- and
   88-colors.

   The 256-color extension came first. 88-colors (using the same control
   sequence) came next, to reduce the amount of memory needed. XTerm
   stores both foreground and background color indexes for each cell on
   the screen. That is two bytes, which doubled the amount of memory used
   by xterm for the scrollback. More important, however, was the number of
   entries in the colormap. With 256 colors, 65536 entries might be used,
   but 88 colors use at most 7744 entries. In the late 1990s, inexpensive
   displays were far less capable, requiring workarounds to get acceptable
   performance.

   The 256- and 88-color schemes (a 16-color table of ANSI (or aixterm)
   colors, followed by a cube and then a grayscale “ramp”) are similar. An
   intermediate 157-color scheme could have been provided,

   88 157 256      Usage
   16  16  16 ANSI/AIX
   64 125 216 cube
    8  16  24 grayscale "ramp"

   but the savings in the colormap would be less compelling:

   Colors Size  Bits
       88  7744   13
      157 24649   15
      256 65536   16

   Like the aixterm 16-color extension, these colors are stored in an
   array. Unlike aixterm (whose developers invented a new set of escape
   sequences not found in ANSI or ECMA-48), we used sequences found in
   ECMA-48: SGR codes 38 and 48. However, the feature evolved:
     * The default color palette for xterm uses header-files generated
       using scripts similar to the ones provided for demonstrations
       (patch #112).
       The first 16 colors (except for blue) use names in the X rgb.txt.
     * The X libraries cannot handle enough resources to specify all of
       the 256 colors as well as other features in xterm.
       Starting with patch #129, I made the resource settings for colors
       past the first 16 a compile-time option. If you prefer to have the
       colors as X resource values, you lose UTF-8. Since xterm accepted
       escape sequences for setting the palette, this was not a problem.
     * Steve Wall modified the palette in 2002 (patch #166), making it a
       little brighter.
     * We used semicolon (like other SGR parameters) for separating the
       R/G/B values in the escape sequence, since a copy of ITU T.416
       (ISO-8613-6) which presumably clarified the use of colon for this
       feature was costly.
       Using semicolon was incorrect because some applications could
       expect their parameters to be order-independent. As used for the
       R/G/B values, that was order-dependent. The relevant information,
       by the way, is part of ECMA-48 (not ITU T.416, as mentioned in Why
       only 16 (or 256) colors?). Quoting from section 5.4.2 of ECMA-48,
       page 12, and adding emphasis (not in the standard):

     Each parameter sub-string consists of one or more bit combinations
     from 03/00 to 03/10; the bit combinations from 03/00 to 03/09
     represent the digits ZERO to NINE; bit combination 03/10 may be used
     as a separator in a parameter sub-string, for example, to separate
     the fractional part of a decimal number from the integer part of
     that number.
       and later on page 78, in 8.3.117 SGR – SELECT GRAPHIC RENDITION,
       the description of SGR 38:

     (reserved for future standardization; intended for setting character
     foreground colour as specified in ISO 8613-6 [CCITT Recommendation
     T.416])
       Of course you will immediately recognize that 03/10 is ASCII colon,
       and that ISO 8613-6 necessarily refers to the encoding in a
       parameter sub-string. Or perhaps you will not.
       It took several years for this to become an issue. The developers
       of other terminal emulators were not the ones who first complained
       about it. In fact, though the order-dependence was mentioned, no
       one pointed to a specific program which was affected. Still, it was
       a known problem.
       Later, in 2012 (patch #282), I extended the parser to accommodate
       the corrected syntax. The original remains, simply because of its
       widespread use. As before, it took a few years for other terminal
       developers to notice and start incorporating the improvement. As of
       March 2016, not all had finished noticing.
       On releasing ncurses 6.1 in 2018, I used the corrected syntax in
       the xterm-direct terminal description, and also provided working
       examples for the other terminals which supported the direct color
       feature. Some of those still did not support the standard syntax
       for the control sequences:
          + xterm+direct is the building-block for standard terminals
          + xterm+indirect is a building-block for nonstandard terminals
       Still later, in 2020, a user's request prompted review of this
       area:
          + One of the other terminal developers had implemented a new
            feature using xterm's original semicolon delimiters.
          + That created a problem for this user because the same string
            sent to both terminals would color text on the other terminal,
            but reset colors on xterm.
          + That happens because (unless xterm were specially modified),
            xterm cannot tell that the new feature has subparameters which
            are supposed to be used for setting colors.
          + The feature itself is nonstandard, using a code marked in
            ECMA-48 for future standardization, so there is no reason to
            modify xterm.
          + As noted in the ncurses FAQ Why not just use TERM set to
            "xterm"?, sometimes xterm's terminal description uses features
            not supported by other terminals.
          + ncurses has correct terminal descriptions for xterm and other
            terminals (such as the one with the nonstandard feature).
          + Providing a terminal description using the nonstandard
            semicolon for delimiting subparameters encourages users to
            stumble into this problem.
          + Going forward (e.g., xterm patch #357), these terminfo
            building blocks are used in ncurses:
               o xterm+256color2 is the building-block for standard
                 terminals
               o xterm+256color is a building-block for nonstandard
                 terminals

   As others incorporated the xterm 256-color feature, the ability to set
   the palette was usually not done before announcing that a program had
   the 256-color feature. Others acquired the ability to set the palette
   after a lapse of years. As an exception, Geoff Wing (rxvt developer)
   implemented the complete feature in August 2002 (release 2.7.9). Any
   xterm-compatible implementation with support for 256-colors
   automatically supports 88-colors, since the palette is modifiable,
   which makes comments such as this at best badly informed.

   XTerm stores the colors for colorUL, etc., at the end of the color
   array used for ANSI, 16-, 88- and 256-colors. An application can modify
   the colors using OSC 4, which does not reduce the range available for
   the SGR 38/48 index used for selecting colors (underline, bold, reverse
   — and italics — all have their place in the video attribute fields).
   Like dynamic colors, this was a feature found in XFree86 but not in
   X11R5 or X11R6. According to David Dawes, some people liked the
   feature. Mark J Olesen incorporated the same into rxvt mid-1996, and I
   added the other two attributes. However, it was mainly popular with Red
   Hat users who wanted to color their manpages. After Werner Lemberg
   changed groff behavior in 2001 to color manpages, this feature is not
   that well known.

   Finally, there are the default foreground and background colors set
   using SGR 39/49.

   If one wants to enumerate the colors which can be set by index in
   xterm, there are multiple indices that are needed:
     * SGR number (for the 8 ANSI colors, the extra 8 aixterm colors and
       the default colors)
     * SGR 38/48 with (index) parameter (for the 88-colors and the
       256-colors, keeping in mind that those include the first 16 ANSI
       and aixterm colors)
     * OSC 4 with (index) parameter (colored video attributes)
     * OSC numbers 10-19 (dynamic colors)

   The sample scripts in xterm's sources demonstrate these features. Some
   are written in POSIX shell, the remainder are in Perl.

    I don't like that shade of blue

   Nobody does. But there are no universal solutions.

   If your terminal (or the application running in it has a dark
   background, then darker blues are hard to see. With a light background,
   yellows are hard to see.

   The available standards do not help: there are no standards for
   terminal colors. Here is an illustration which I made in reply to a bug
   report, contrasting different choices for blue, against some of the
   other terminals which (were said to) provide "standard vt100 colors":

     Contrasting blue in terminal emulators

   Of course, anyone developing a terminal emulator already knew that
   vt100's never did do colors.

   Ultimately it is up to the application running in a terminal to enforce
   the colors it needs. XTerm merely provides the best compromise on
   default visibility that I and my users have found.

    Why doesn't xterm support italics?

   Well, actually it does and it doesn't.

   You can display "any" font using xterm (though proportional fonts may
   be disappointing).

   But xterm has specific types of graphic rendition that it will do. If
   you want italics, then xterm has an option (italicULMode) to use that
   rendition instead of underlining. That is the usual typographic
   alternative, though of course some people want both at the same time.

   However, standard curses does not support italics. Few terminals do
   this reliably, so it was disregarded long ago, never was supported
   except for low-level applications (in terminfo). No bit was reserved in
   the curses header for adding italics for high-level applications. (As a
   special case, ncurses was modified to provide partial support, but
   programs using this feature will not work with other implementations).

   XTerm stores each cell of the display in fixed-size structures. One
   byte stores the graphic rendition. XTerm is using all of the bits in
   this byte for its VT220 emulation:

   Mnemonic  Bit                 Description
   INVERSE   0   show cell reverse-video
   UNDERLINE 1   show cell underlined
   BOLD      2   show cell as bold
   BLINK     3   show cell as blinking
   BG_COLOR  4   use background color
   FG_COLOR  5   use foreground color
   PROTECTED 6   character cannot be erased
   CHARDRAWN 7   character has been drawn here on the screen

   While additional bytes could be added to each cell, the cost to the
   typical user has so far not been in line with the usefulness of the
   feature.

   For those who are not constrained by cost, since patch #305 xterm
   provides an experimental compile-time option to support italics. The
   main reason for implementing this is to be able to test the italics
   feature added in ncurses (patch 5.9.20130831):
     * this increases the size of the attributes data.
     * the feature requires some overhead for font-switching (treating
       italics as "rare")

   The increase in size is not entirely wasted. The SGR attributes for
   dim, strike-out, and double-underscore also are implemented. However,
   the last two are not in the portable terminfo definition (from X/Open),
   and are not supported in the higher-level curses interface (there is no
   A_STRIKE for that reason).

   Here are screenshots showing the ncurses test-program displaying video
   attributes (including italics). The first uses bitmap fonts:

     ncurses – video attributes with bitmap-font

   and the second uses a (same size) TrueType font:

     ncurses – video attributes with TrueType font

    "grep --color" does not show the right output

   GNU grep (version 2.5) introduced a --color option.

   It does this for each highlighted match:
    1. it writes the text up to (not including the match)
    2. it writes an ANSI color control control sequence
    3. it writes the matched text
    4. it writes a control sequence to clear to the end of the line
    5. it writes an ANSI control sequence to reset graphic rendition.
    6. repeat this process until the entire line is written.

   One problem is in the second and fourth steps. If the preceding text
   brought us up to the last column, then xterm (and any VT100-compatible
   terminal) is waiting for graphic text to wrap to the next line. Any
   controls would take effect on the current column position. Newlines are
   ignored while in this state.

   However, if xterm gets a control sequence while waiting to wrap to the
   next line, it will update the screen according to that control. Then it
   is ready to accept more data. But at this point, it is no longer
   waiting to wrap; the special case is for newline versus graphic
   characters. For instance, backspacing clears the state (vttest
   illustrates this). So the data starts to write at the current column
   (the last one on the line), rather than at the beginning of the next
   line. In that case, grep's output will not look right.

   Here are some relevant bug reports:
     * Debian #456943 - grep: incorrect display with color and wrapping in
       some terminals
     * Fedora #1006310 - xterm does not print a character if the character
       is last on a row and a color-change ANSI sequence follows
     * Novell #148844 - terminal text wrapping bug

    That description of wrapping is odd, say more?

   This is one of the aspects of the so-called "vt100 glitch", as
   mentioned in the terminfo manpage:

     Terminals which ignore a line-feed immediately after an am wrap,
     such as the Concept and vt100, should indicate xenl.

   When the terminal reaches the right margin, it is in a special state
   where it ignores tab characters and other formatting controls (carriage
   return and newline), and in effect is expecting only printable
   characters to wrap to the next line.

   Without it, it is misleading to refer to a terminal as a vt100
   emulator. After all, it is a well-known feature named for the VT100.
   The applicable standards (ISO-6429, ECMA-48) do not go into enough
   detail to address this sort of behavior, so the other terminal
   emulators can be referred to most accurately as ANSI terminals (if they
   obey the other guidelines).

   In 2004, I added a test-screen to vttest to demonstrate this. It was in
   response to someone who insisted that xterm was wrong and one of those
   other terminal emulators was "right". I investigated, found that the
   behavior had not changed in xterm at least since the early 1990s, and
   that it matched the description of behavior from the DEC manuals. One
   of my users verified the correctness of the test on a VT520.

   Reviewing the results with xterm-alikes or less ambitious "vt100
   emulators" in mid-2013:
     * xterm, kterm, mlterm, some operating system consoles are consistent
       with the VT100 behavior.
     * rxvt, screen, putty (pterm), konsole, vte (gnome-terminal,
       xfce4-terminal) are not consistent with VT100 (and behave
       differently compared to each other).
       I included screen here because it claims to be a vt100 emulator,
       and putty since it claims to be an xterm emulator. I did not
       include tmux, because it does not make either claim.
     * mrxvt does not get to that screen; it resizes its window to a
       single line.

   In the vttest page, I have provided screenshots to illustrate these
   points.

   Since 2013, Mattias Engdegård created a test program to explore this
   area, citing DEC's internal standard document for terminals (DEC STD
   070 Video Systems Reference Manual). That document refers to this as
   the last column flag.

   Revisiting this in 2019, no improvement has been observed in the
   problematic programs from 2013. A VTE user gave this example

     #!/bin/bash
     echo -e "\e[2J"
     echo -e "\e[1;79Hx\b\vx\b\vx\n"
     echo -e "\e[5;80Hx\b\vx\b\vx\n"

   In this case, DEC's documentation for the last column flag mentions
   that cursor-positioning resets the flag. Because xterm takes that into
   account (while the others from 2013 do not), the example will show
   different results. Markus Schmidt provided a screenshot which
   demonstrates that DEC's documentation is correct and that some terminal
   emulators (e.g., xterm, zoc, MacOS Terminal, st) implement this detail
   in the same way that the hardware terminal did:

     screenshot of last column flag with cursor positioning

    That color scheme is odd, say more?

   Occasionally someone questions the behavior of the bce (background
   color erase) feature in xterm, and mentions that some DEC terminal did
   not behave that way with ANSI colors.

   First off:
     * Aside from the VT525, DEC terminals had no support for ANSI colors.
     * Likely, they were thinking of a terminal emulator which supported
       colors. A while back, there was more than one which said they were
       a “VT340” and the misconceptions began. Not all of those behaved
       the same.
       Some developers were aware of this, others were not. The
       comp.os.vms newsgroup thread How to setting color in code for a VT
       terminal shows both.
     * From the outset, modern xterm was a VT100 or VT220 with ANSI
       colors. No technical manual was available for a VT525 at the time.
       Lacking a technical manual, information about a VT525 was no more
       reliable than the statements about a VT340.

   The design used for xterm imitated Linux console, which itself came
   about from different people (see this page for some background).

   The VT525 programmer's reference manual is vague on the details (ANSI
   color is mentioned in a fraction of one percent of the manual), but the
   DEC standard for terminals is clear that it would not implement bce:
   any erase command will reset the video attributes. It documents ANSI
   color in the section on video attributes without mentioning a special
   case. Color would be reset as well.

  Odd behavior

    Why can't I select/paste in xterm?

   When an application sets xterm to any of its mouse tracking modes, it
   reserves the unshifted mouse button clicks for the application's use.
   Unless you have modified the treatment of the shifted mouse button
   events (e.g., with your window manager), you can always do select/paste
   by pressing the shift key while clicking with the mouse.

   This is all done using the translations resource (see the Default Key
   Bindings section in the manual page).

    Why can't I select/paste to/from other programs?

   Whether you select text in xterm and paste into another window, or the
   reverse, the X client in which you have selected text may provide the
   data in different formats and different containers:

   formats
          Originally (and by default) xterm made the selected data
          available with ISO-8859-1 encoding (Latin-1). Since patch #101
          (1999), it has provided it also in UTF-8.

          Regarding the type of data:

          + X11R4's ICCM documented "string" selection data with
            ISO-8859-1, while
          + X11R6 documented "compound text" (another name for multibyte
            encoding, without specifying what encoding).
          + Selection data using UTF-8 was an extension by XFree86.

          The client holding the selection advertises the formats that it
          can provide, and other client(s) ask for it using one of those
          formats.

          Xterm can ask for UTF-8 even if it is not configured to use
          UTF-8. In that case, it converts (a small number of) useful
          characters to their ASCII or VT100 line-graphics equivalents,
          and uses a "#" character for those which cannot be converted.

   containers
          By default, xterm follows the Inter-Client Communication
          Conventions Manual (ICCM). That dates back to X11R4 in 1989,
          with minor updates in 1996 for X11R6. The copyright for ICCM 1.0
          is 1988/1989, making it slightly older than Microsoft Windows.

          The ICCM specifies "selection atoms" which are maintained by the
          X server. According to the ICCM:

     The selection named by the atom PRIMARY is used for all commands
     that take only a single argument and is the principal means of
     communication between clients that use the selection mechanism.

          and

     The selection named by the atom CLIPBOARD is used to hold data that
     is being transferred between clients, that is, data that usually is
     being cut or copied, and then pasted.

          xterm uses PRIMARY by default. The default translations also
          update something called CUT_BUFFER0 (also part of the ICCM).

          Unlike the PRIMARY selection, a cut buffer can hold only "type
          STRING and format 8" (which happens to be ISO-8859-1). That
          sounds like a drawback, but on the other hand, cut buffers are
          persistent, while the PRIMARY selection is not. An X client can
          provide data using the PRIMARY selection only as long as it
          holds the selection.

   If xterm does not own the selection, it cannot supply the data (and you
   cannot select/paste). Initially, xterm held the PRIMARY selection only
   as long as the text was highlighted. Another application could assert
   the selection, but generally losing the PRIMARY selection in xterm was
   the same as losing highlighting. That has been improved, e.g., using
   the keepSelection resource in patch #230 (2007), as well as refinements
   to retain highlighting when it updates other parts of the window.

   A more likely reason for failing to select/paste is that the other
   application may not use the same selection atom (container). In the
   mid-1990s, Netscape set out to compete with Internet Explorer. Part of
   that involved copying many aspects of the way Internet Explorer worked,
   including the way it worked with the Microsoft Windows clipboard.
   Netscape on non-Windows platforms, "of course" assumed the clipboard
   was the way to do things, and used the X11 clipboard rather following
   the ICCM. (The way it used the X11 clipboard was also not in line with
   the ICCM, but it was "close").

   Not all applications followed Netscape and its descendents, making it a
   nuisance if one wanted to select/paste text to/from the web browser.

   Since patch #209 (2006), xterm has provided a workaround: a menu entry
   (and resource selectToClipboard) which changes xterm's behavior for a
   special token SELECT in its default translations. If the resource is
   true (or the menu item enabled), xterm provides its selection to the
   CLIPBOARD. A menu item is provided, of course, since many applications
   follow the ICCM. In the default translations, these lines use SELECT:

Shift <KeyPress> Select:select-cursor-start() \
                           select-cursor-end(SELECT, CUT_BUFFER0) \n\
Shift <KeyPress> Insert:insert-selection(SELECT, CUT_BUFFER0) \n\

    Why can't I select tabs in xterm?

   This issue was noted early on, here in 1997.

   XTerm is copying from the screen, which stores only printable
   characters. That includes spaces and line-drawing characters. But tabs
   are special; they are used for more than one purpose.

   If the screen is cleared in some part, that stores nulls. Cursor
   addressing does not fill in nulls as it jumps around, though xterm does
   supply blanks for the most useful cases, especially when getting data
   for a selection.

   Full-screen programs such as text-editors tend to write in random
   fashion, and generally do not print nulls to the screen. Curses on the
   other hand, may supply tabs where you thought there were none. Also,
   the terminal driver can expand tabs (and often is set to do this by
   default).

   So the whole thing is unreliable: unless you make special arrangements
   for each of the programs running inside xterm, you would often get a
   tab when you expect, and vice versa.

   For the special case where your expectations would match the available
   data, it is solvable. There are basically two ways it could be done:
     * set a bit in each cell's data which says it was skipped over via a
       tab. The complication is that xterm is using all of the flag bits
       in each cell.
     * store literal tabs and nulls to be interpreted later – both by the
       display and the selection logic.

   As of 2010, a few other terminals do implement this feature. But the
   reason that it's been low-priority is that it's of very limited
   usefulness when copying between terminal sessions (and for that matter,
   from other clients).

    FVWM does weird things when I try to resize xterm

   I have an old (3.1.2G) bug report for xterm which may be related to the
   second (3.9s) problem:
     * Steven Lang <tiger@ecis.com> reports a problem with extra resize
       events for xterm.
       When I change font size often I will get the double-refresh, and
       when that happens the text program gets 2 resize events.. Running a
       quick test, I got this: Going to a bigger font, it got a 53x20
       resize, then a 80x24 resize. Going to a smaller font, it got a
       120x27 resize, then a 80x24 resize.
       Earlier I made a mention of changing font size in rxvt (And xterm
       does it to) causing 2 resize events. Well I just happened to do it
       in fvwm (Instead of fvwm 95) and found it seems to be a 'feature'
       of fvwm95, not XFree86 as I'd initially assumed.
     * Stephen Marley <stephen@memex.com> reports a problem with the
       active icon (from X11R6.3 xterm):
       Using the XFree86 xterm-53 with the active icon feature on, I get
       some problems resizing where the xterm window shrinks as small as
       possible and won't stay at whatever size you set it thereafter.
       Comment out the PixmapPath and IconPath from your .fvwmrc file to
       disable the fvwm icons and restart the WM. Start an xterm. Iconify
       xterm and maximize it again. Use resize button or corners to resize
       the xterm.
       The xterm now shrinks to a tiny size and attempts to resize it
       result in it shrinking again.
       I've tried this with fvwm 1.23 and fvwm 2.0.46 with the same
       results. Olvm, olvwm and twm all behave correctly so it may be a
       fvwm problem.

   I have not observed the first, but have reproduced the second.

    Why doesn't the screen clear when running vi?

   This refers to the "alternate screen" feature, which has been used in
   its termcap file since 1988. On various systems, this feature may have
   been removed, although it has always been in the xterm sources.

   The feature is controllable (it can be enabled or disabled). However,
   as it was originally conceived, that ability to control it applies only
   to programs using termcap.

   Under SunOS 4.x, the termcap description for xterm embeds in the ti and
   te capabilities a command to switch to xterm's alternate screen (e.g.,
   while running vi), and return to the normal screen on exit. This has
   the effect of clearing the screen. The corresponding terminfo symbols
   for ti and te are smcup and rmcup, respectively.

   Beginning with Solaris 2.x, the terminfo description did not use the
   alternate screen (it is a matter of preference after all), so that the
   text from vi remains on the screen after exit. Sun patched the X11R5
   terminfo description to omit the smcup and rmcup capabilities. However,
   Sun began distributing modern xterm on the freeware companion (a CDROM)
   beginning with Solaris 8. In Solaris 10 for instance, the ncurses 5.6
   package provided a usable terminal description for xterm which uses the
   alternate screen. Solaris 11 distributes modern xterm (though perhaps
   oddly) using an old—unpatched—terminal description.

   Because it is in the terminal description, the feature is
   configurable...

   For example (from Bjorn Helgaas <helgaas@dhc.net>) this procedure adds
   these capabilities to the "xterm" terminfo definition on HP-UX 10.20:

     cp /usr/lib/terminfo/x/xterm /usr/lib/terminfo/x/xterm.orig
     untic xterm > /tmp/xterm.src
     echo " smcup=\E7\E[?47h, rmcup=\E[2J\E[?47l\E8," >> /tmp/xterm.src
     tic /tmp/xterm.src

   In this example, the terminfo strings are a series of operations:

   smcup
          \E7 saves the cursor's position
          \E[?47h switches to the alternate screen

   rmcup
          \E[2J clears the screen (assumed to be the alternate screen)
          \E[?47l switches back to the normal screen
          \E8 restores the cursor's position.

   However, xterms that are linked with termcap are more flexible in this
   area than those linked with terminfo libraries. The xterm program
   supports a resource titeInhibit which manipulates the $TERMCAP variable
   to accomplish this. It sets the $TERMCAP variable for the client with
   the ti and te capabilities suppressed. Systems that use terminfo cannot
   do this. If you are running terminfo with the alternate screen controls
   in the terminal description, then you can suppress the switching to the
   alternate screen by the titeInhibit, but not the associated cursor
   save/restore and clear-screen operations.

   XFree86 3.9s xterm implemented a different set of controls (private
   setmodes 1047, 1048 and 1049) which address this (in addition to the
   older set of controls, for compatibility). The new set of controls
   implements the entire ti sequence (save cursor, switch to alternate
   screen, clear screen) and te (switch to normal screen, restore cursor)
   as two control sequences that can be disabled by titeInhibit.

   The 1049 code is a refinement of 1047 and 1048, clearing the alternate
   screen before switching to it rather than after switching back to the
   normal screen. Since patch #90 in 1998 xterm allows you (with a popup
   menu entry designed to exploit this behavior) to switch the display
   back to the alternate screen to select text from it, to paste into the
   normal screen. You can also set or clear the titeInhibit resource using
   another popup menu entry (Enable Alternate Screen Switching).

   Most other terminal emulators implement only half of the feature. They
   recognize the control sequence, but do not provide the ability to
   change it at runtime, e.g., using a menu entry. Like any other
   half-done implementation, that is a bug which should be reported to the
   developers of those programs.

    Why doesn't the screen clear when I type control/L?

   Control/L is ASCII form-feed. Printers do something with form-feed.
   Terminals do not, as a rule (though I agree it would be nice, e.g.,
   this).

   Interpreting form-feed is normally done by your shell, not by the
   terminal emulator. In a quick check:
     * bash, tcsh, zsh interpret form-feed by clearing the screen, while
     * csh, dash, ksh, mksh, yash do not

   VT100s did not respond to form-feed. A few terminal emulators interpret
   form-feed (PuTTY and SunOS console), but neither matches VT100
   behavior.

   Because most people do not see the difference between a form-feed which
   they type (and is presumably echoed as a form-feed) versus a form-feed
   which is sent from an application to the terminal, this leads to
   confusion. Several years ago, I pointed this out as one of the errors
   in the C FAQ (notwithstanding Summit's comment, he did not update the
   FAQ).

    Why is the cursor misplaced after running vi?

   Vi and other full-screen applications use the termcap ti/te (terminfo
   smcup/rmcup) strings to initiate and end cursor addressing mode. As
   mentioned in the discussion of titeInhibit, full-screen applications
   can expect the initialization string to save the cursor's position, and
   the end-string to restore it.

   A few applications (reportedly IRIX 5.x and 6.x vi incorrectly move the
   cursor before initializing cursor-addressing. This will cause the
   end-string to restore the cursor to its position when it was saved by
   the initialization string (typically at the upper left corner of the
   screen).

   The usual reason is due to the cursor save/restore controls in the
   ti/te strings. If your application runs a subprocess which in turn runs
   another full-screen application (or when reinitializing the screen
   after the shell process), it will save the cursor position again, so
   the position which is restored when finally exiting your program is the
   last one saved, not the first. Modern xterm (from late 1998, patch 90)
   changes the behavior of the cursor save/restore operations so they
   apply only to the current screen. That makes it less likely to misplace
   your cursor.

    Why doesn't the scrollbar work?

   Originally xterm was built using imake rather than a configure script.
   One feature of imake that is not possible to guess within the configure
   script is the wide-prototype compile-time definition NARROWPROTO. When
   this is not set properly, the Athena widget scrollbars do not work
   properly. xterm's configure script has a fallback case which allows
   disabling imake. However, this is moot with the Xorg "modular" build,
   whose compiler options are unrelated to imake or older versions of any
   libraries that it may distribute. In this case, the configure script
   needs some help. Use this option to enable or disable NARROW proto (and
   disable imake with the --disable-imake option) to match the whims of
   Xorg hackers.

   For instance

configure --disable-imake --disable-narrowproto

    Can I improve the scrollbars?

   Is that a problem with the appearance, or the way they work?

   The appearance can be modified (though few do this) by linking with one
   of the variants of the Athena widget set (Xaw).

   To illustrate, here are a few screenshots:

   Xaw (default)
          xterm – default scrollbar with Xaw

   XawPlus
          xterm – scrollbar with XawPlus

   Xaw3d
          xterm – scrollbar with Xaw3d

   neXtaw
          xterm – scrollbar with neXtaw

   Those variants use the same calling interface, so supporting them is
   simple. Adapting to other toolkits would be much more difficult. For
   instance (see the discussion of mxterm), replacing the scrollbars may
   require replacing other parts from the library to get consistent
   initialization and operation. In the case of Motif, it had nothing like
   the Athena widget set's popup menus.

    Can I improve the scrolling speed?

   Several years ago (before 2010) there was a webpage which gave its
   author's notion of what constituted a “good” terminal emulator: cat'ing
   (sending) a large file to the terminal would complete in minimal time.
   Apparently that was the sole interest. Interestingly, its author stated
   that xterm was the slowest although the presented data do not show
   this. Also, although the page says “Linux” some of the data are for
   programs running on Windows. The page spawned a few imitators (with no
   better methodology), none was systematic, none did any analysis.

   Of course, developers do not do that in practice. The terminal is
   useful for interactive tasks. Compiling is best done by redirecting the
   build messages to a log file or using a batch process. End users have a
   different outlook.

   There is more than one factor involved in scrolling speed. Here are a
   few:
     * When xterm was first written, machines had less memory, and
       scrolling back a thousand lines seemed good enough for users.
       Internally, xterm stored the current screen and saved-lines in a
       large array. It scrolled the array by shifting the entire array by
       a given number of rows. For a thousand lines saved-lines (the
       scrollback region), that works well enough.
       But the saveLines resource allows a full integer, and during the
       mid/late-1990s, a few users found that setting the resource to a
       million lines made xterm very slow.
       Still, the graphics display was fast enough. By the way, xterm uses
       the XCopyArea function, and normally (attempts to) display all of
       the updates to the screen.
     * Later, rxvt came along. It limited the number of saved-lines to a
       signed 16-bit integer, i.e., 32767 (and some packagers limited it
       to only a few thousand lines), and moved just the pointers to the
       line data when scrolling rather than shifting all of the text. It
       also uses XCopyArea, noting in its features

/*
 * Define to remove support for XCopyArea() support.  XCopyArea() is useful
 * for scrolling on non-local X displays
 */
/* #define NO_SLOW_LINK_SUPPORT */

       Unlike xterm, rxvt did not attempt to display all updates. If it
       fell behind, it would discard some of the updates, to catch up.
       Doing that had a greater effect on the apparent scrolling speed
       than its internal memory organization, since it was useful for any
       number of saved-lines. One drawback was that ASCII animations were
       somewhat erratic.
     * A few other terminal emulators, such as konsole copied the rxvt
       feature. Others copied, in turn, from whatever source. As a result,
       one cannot compare the speed of different terminal emulators, since
       they do not follow the same rules.
     * The issue with xterm shifting a large array was a problem which was
       addressed by changing all of the pointers to its line data into a
       circular array in 2009 (patch #244).
     * Even after improving the memory performance of scrolling, rxvt and
       its imitators still appeared to scroll faster.
       The fastScroll resource added in patch #244 provides a simple
       implementation of the rxvt (mis?)feature for xterm.
       As implemented, it is rather crude (sometimes xterm — like konsole
       — appears to stop, since it is waiting for a new set of screen
       updates after having discarded some).

   Scrolling speed is only one aspect of terminal speed, but it is easy to
   measure. Other aspects (such as the speed with which an application can
   change color, move the cursor around the screen, write text in various
   places) can also be measured. But comparing terminals based on that
   speed can be misleading. When the terminal drops updates to keep up
   with an application's speed, the result may be unnoticeable (if the
   application is fast enough), or it may not.

   For example, running the dots program from the ncurses-examples shows
   some interesting misbehavior with gnome-terminal and konsole: both
   “choke” at times for a few seconds. The dots program prints colored
   cells randomly around the screen, pausing briefly 1% of the time.
   However when dots is terminated, it prints the program's notion of the
   output rate. In spite of the pauses, the program saw a fairly good rate
   of output. Some terminal emulators cannot keep up with dots; one
   possible explanation for the discrepancy is that the terminal emulator
   discards output (as in the special case of scrolling).

   Seeing that raised the question of what variation to expect from
   different terminal emulators, to point out which might discard output
   to achieve fast scrolling speeds. A simple script showing the elapsed
   time to send ncurses's terminfo.src (1.1Mb) a given number of times to
   the terminal was used. Here is a table illustrating the differences,
   using the available terminal emulators for Fedora 26 and Ubuntu 17 in
   November 2017:

    Mode       Terminal          Fedora        Ubuntu
                              1    10   99   1    10   99
   Remote gnome-terminal     (1)  (1)  (1)  (1)  (1)  (1)
          konsole            0.12 2.10 23.2 0.26 2.65 25.7
          mlterm             (2)  (2)  (2)  0.30 3.07 30.4
          pterm / putty      0.15 1.42 14.6 0.55 5.66 56.2
          rxvt (3)           0.25 2.97 29.5 0.23 3.03 29.5
          st / stterm (4)    0.07 0.50 4.40 0.15 1.42 14.4
          terminology        0.10 1.00 10.1 0.19 2.01 19.0
          urxvt              0.05 0.38 3.24 0.17 1.60 15.7
          xterm              0.31 3.50 34.8 0.47 4.41 44.1
          xterm + fastScroll 0.09 0.82 8.36 0.39 2.43 22.9
   Local  gnome-terminal     0.12 1.16 11.4 0.29 3.14 30.6
          konsole            0.11 0.82 7.97 0.22 2.17 20.1
          mlterm             (2)  (2)  (2)  1.01 7.59 105.
          pterm / putty      0.17 1.52 14.6 (5)  (5)  (5)
          rxvt               1.23 11.9 118. 1.75 16.9 166.
          st / stterm (4)    0.08 0.61 5.10 0.21 1.63 15.9
          terminology        0.09 1.03 10.1 0.43 1.64 16.0
          urxvt              0.07 0.53 4.52 0.26 2.41 23.7
          xterm              1.77 18.5 178. 2.70 26.5 259.
          xterm + fastScroll 0.12 0.96 9.92 0.25 2.36 22.9

   Notes:
    1. On both systems, gnome-terminal failed to connect remotely.
    2. Fedora does not have mlterm.
    3. On Ubuntu, the urxvt package hijacks the name “rxvt”, so the “rxvt”
       actually tested was rxvt-xpm from the rxvt 2.7.10 package.
    4. Fedora has st 0.70, while Ubuntu has version 0.60, which is a
       couple of years older.
    5. Running locally on Ubuntu, pterm 0.70-1 dumped core.

   Regarding the selection of terminal emulators:
     * Keeping mind that this is an xterm FAQ, the Linux console (and
       Windows console, and PuTTY running on Windows) are off-topic.
     * The table mentions programs which at one time or another have set
       TERM=xterm.
       The actual test does not rely upon the terminal description, nor in
       fact on any terminal description. The distinction was made for
       their relevance to this FAQ.
     * Given that, rxvt 2.7.10 is listed, as well as its descendent urxvt
       (rxvt-unicode).
       Other variations of rxvt (such as aterm and mrxvt) were considered,
       but since much of the related code is identical, not very
       interesting.
     * Both systems have several variants of the skins for the VTE
       library, but for both systems, the developers have a heavy bias in
       favor of the GNOME desktop. Comparing the performance of the
       various skins would be pointless, since not all are equally
       supported (due to the GNOME developers' practice of making
       incompatible changes), and would make an unbalanced comparison in
       any case.
     * The Unix port of PuTTY, pterm is listed. It uses GDK.

   Interestingly, performance is better running remotely. In the test, the
   machines are not identical:
     * The remote system uses a Mac mini-server.
     * The Fedora system is a virtual machine using Parallels.
     * The Ubuntu system is a virtual machine using Vmware Fusion.

   Possibly displaying on the virtual machines does not perform as well as
   via XQuartz. But that is a lot of difference to explain. More likely,
   the local X server is performing badly on some calls.
     * For a while, XCopyArea was a problem, where the Xorg hackers had
       degraded its performance radically. While that might still be the
       underlying issue, st and urxvt do use that function.
     * Another possibility is mentioned in Why is the text in the wrong
       place? where the apparent root cause was a server feature which
       only implemented parts of the X protocol.

   Using the fastScroll feature made xterm performance comparable to the
   “desktop” applications. But as usual, with performance data, your
   mileage may vary.

    Why can't my program read the window title?

   The longstanding control sequence for reading the window title is
   something that can be abused in special conditions. For novice
   (unknowledgable) users, this can be a problem.

   XTerm provides resource-settings and menu entries to allow this and
   related features to be enabled or disabled. See for example
   allowWindowOps The default resource settings in xterm can be overridden
   by a packager. However, a knowledgable user can override those default
   settings.

   It is also possible that an overzealous packager may have crippled
   xterm by removing the functionality altogether. (That should be
   reported as a bug, to me).

   For instance, one of those sent me a "security fix" some years ago,
   which deleted most of the control sequences which return data to the
   host. It broke the resize program, and selection, among other uses
   considered to be benign. In contrast, the same features used in other
   terminal emulators are tolerated by the same people, so rather than
   being a misguided attempt at fixing security issues, patches such as
   that appear to be an attempt at harassment.

    Why can't my program set the window size?

   Some overzealous packagers, perhaps influenced by the demonstration I
   provided, are protecting you against the possibility of your xterm
   becoming inaccessible. (That's unlikely...).

   You should be able to override it, as noted above via resource settings
   or menu entry ("Allow Window Ops").

    Why is the text in the wrong place?

   Are you using Ubuntu? This is a frequently-reported problem for Ubuntu
   users. With other systems, it can occur (as of September 2012), but is
   less frequent. But it has been an issue with Ubuntu since 2008.

   There are several related symptoms, e.g.,
     * text may be the wrong size
     * repainting the screen puts text in the wrong place

   Here are some of the corresponding bug reports:
     * Ubuntu #199285 - xterm crashes when compiz is on
     * Debian #467399 - compiz fails to take control of windows
     * Ubuntu #378668 - Cursor in terminal behaves badly with special
       characters present
     * Novell #622936 - xterm: font drawing glitch
     * Redhat #583904 - gnome-terminal and xterm show garbled fonts with
       compiz enabled (intel graphics)
     * Redhat #614542 - xterm graphical corruption when compiz is active
     * Ubuntu #635258 - Garbled chars in xterm
     * Ubuntu #644943 - xterm fonts get corrupted while typing
     * Ubuntu #701160 - /usr/bin/xterm is not functional in natty
     * Ubuntu #700477 - Font corruption in xterm under Lucid
     * Novell #681359 - xterm: no data shown under the screen program
     * Ubuntu #711894 - iconic option does not work with compiz
     * Ubuntu #778439 - Typing "exit" in xterm kills X session
     * Ubuntu #831336 - running 'xterm' crashes X server
     * Ubuntu #841103 - Text has artifacts when typing something else
     * Ubuntu #844454 - Garbled chars in xterm (Onieric)
     * Ubuntu #1002972 - xterm moves to upper left when clicking titel bar
     * Ubuntu #1007722 - xterm doesn't display all the information

   Since the problem is not in xterm, all I can do is to help forward
   those bug-reports to whatever package owns compiz. What these have in
   common is that someone has written code which is tested against only a
   small subset of the X protocol.

   Looking for solutions (since compiz is not being fixed), it is possible
   to disable compiz. The means for doing this vary with time. Aside from
   pointing to the root cause of the problem, there is little advice that
   is useful.
     * For instance, this comment by Eric Williams suggests that the
       problem can be worked around by setting xterm's borderWidth
       resource to zero.
     * other comments suggest turning off the "desktop effects" or
       "animation".
     * On my machines using the default Ubuntu desktop, I can see
       misbehavior easily in Ubuntu 12.04 using vttest. However, Ubuntu
       12.04 provides Ubuntu 2D, which does not show those problems (and
       is noticeably faster).

  Sample .Xdefaults Color-Settings for XTerm

   This example dates from March 1997:

     XTerm*internalBorder:  10
     XTerm*highlightSelection:  true
     XTerm*VT100.colorBDMode:  on
     XTerm*VT100.colorBD:  blue
     XTerm*VT100.colorULMode:  on
     XTerm*VT100.colorUL:  magenta
     XTerm*VT100.eightBitInput:  true
     XTerm*VT100.eightBitOutput:  true
     XTerm*scrollBar:  true
     XTerm*VT100.titeInhibit:  true

     XTerm*VT100.colorMode:  on
     XTerm*VT100.dynamicColors:  on

     ! Uncomment this to use color for underline attribute
     XTerm*VT100.colorULMode:  on
     XTerm*VT100.underLine:  off

     ! Uncomment this to use color for the bold attribute
     XTerm*VT100.colorBDMode: on

     XTerm*VT100.color0: black
     XTerm*VT100.color1: red3
     XTerm*VT100.color2: green3
     XTerm*VT100.color3: yellow3
     XTerm*VT100.color4: blue3
     XTerm*VT100.color5: magenta3
     XTerm*VT100.color6: cyan3
     XTerm*VT100.color7: gray90
     XTerm*VT100.color8: gray30
     XTerm*VT100.color9: red
     XTerm*VT100.color10: green
     XTerm*VT100.color11: yellow
     XTerm*VT100.color12: blue
     XTerm*VT100.color13: magenta
     XTerm*VT100.color14: cyan
     XTerm*VT100.color15: white
     XTerm*VT100.colorUL: yellow
     XTerm*VT100.colorBD: white

     XTerm*VT100.cursorColor: lime green

   XTerm comes with two copies of each resource file, one with color only
   (XTerm-col.ad, which is installed as XTerm-color), and the regular one
   (XTerm.ad, installed as XTerm). To use the XTerm-color file in
   conjunction with a separate XTerm app-defaults file which does not
   contain color, add the following line to your .Xdefaults file:

     *customization: -color

   Since 1997, the resource files grew in size and number. Besides XTerm
   and XTerm-color, there are also resource files for xterm using
   different class values, together with the -color flavors of these.
   Because the -color flavors differ only by an #include statement, the
   makefile generates these from XTerm-col.ad. Here are the others:

       Program   Resource
     xterm      XTerm
     uxterm     UXTerm
     koi8rxterm KOI8RXTerm

   Besides just adding files, I continued testing more resource
   combinations. Originally (in the 1990s for instance), developers could
   reasonably expect their users to configure resources for themselves,
   rather than use a single prepackaged flavor. That was a while ago.
   After 2000, I developed nicer resource files. Rather than modify the
   installed app-defaults file, I use this feature from X:

     Directories named by the environment variable XUSERFILESEARCHPATH or
     the environment variable XAPPLRESDIR (which names a single directory
     and should end with a ‘/’ on POSIX systems), plus directories in a
     standard place (usually under /usr/share/X11/, but this can be
     overridden with the XFILESEARCHPATH environment variable) are
     searched for for application-specific resources. For example,
     application default resources are usually kept in
     /usr/share/X11/app-defaults/. See the X Toolkit Intrinsics – C
     Language Interface manual for details.

   That is, if you set the XAPPLRESDIR environment variable to point to a
   directory, you can put application resource files there, and X will
   find those before the system app-defaults files. That allows more
   flexibility and better control over the various applications than
   putting everything into a single .Xdefaults file.

   On the opposite extreme, some people advise using xrdb. Not everyone.
   Back around 1990 I had an informative conversation with one of the
   developers at the Software Productivity Consortium. He was a member of
   a team developing a set of X widgets. The gist of our conversation was
   that
     * using xrdb prevented you from changing things dynamically.
     * it was like using a hammer (nailing things down to prevent them
       from being different).
     * when the only tool you know how to use is a hammer, all of the
       problems look like nails.
     * a good developer knows how to use more than one tool.

  What is this warning message?

   xterm: Error 11, errno 22: permission denied
          Actually, any message like this denotes a failure which requires
          studying the xterm source to determine the exact problem.

          You have either found a bug in xterm, or there is something
          wrong with your computer's configuration, e.g., not enough
          pty's, incorrect permissions, etc.

          The first number is an internal code (defined in error.h in
          xterm's source), and the second is the system error number
          (defined in /usr/include/sys/errno.h). The system error number
          is easier to lookup, but the internal error code tells you where
          to look in the source.

   input method doesn't support my preedit type
          Ignore this if you do not know what input method is. Input
          methods are used to enter composite characters (e.g., umlauts,
          other types of punctuated characters, East Asian characters,
          etc). Your computer's libraries support this, but are missing
          configuration tables, and xterm is warning you.

          If the message bothers you (e.g., if you aren't starting xterm
          from a window manager menu), you can suppress it by setting a
          resource:

     XTerm*openIm:false

   Warning: Actions not found: ignore, "xxx"
          The action "xxx" (for example "scroll-back") is specified in a
          resource file whose translations match widgets that do not
          support them. For example, this

     XTerm*translations:     #override\n\
             <Leave>, ~Ctrl ~Meta <Btn2Up>: ignore()\n\
             ~Shift <Key>KP_8: scroll-back(1,line)\n\
             ~Shift <Key>KP_2: scroll-forw(1,line)\n\
             Shift <Key>KP_8: scroll-back(1,halfpage)\n\
             Shift <Key>KP_2: scroll-forw(1,halfpage)

          will produce warnings such as

Warning: Actions not found: ignore, scroll-back, scroll-forw
Warning: Actions not found: ignore, scroll-back, scroll-forw
Warning: Actions not found: ignore, scroll-back, scroll-forw

          This is a correct form, assigning the actions to the "VT100"
          widget.

     XTerm*VT100.translations:     #override\n\
             <Leave>, ~Ctrl ~Meta <Btn2Up>: ignore()\n\
             ~Shift <Key>KP_8: scroll-back(1,line)\n\
             ~Shift <Key>KP_2: scroll-forw(1,line)\n\
             Shift <Key>KP_8: scroll-back(1,halfpage)\n\
             Shift <Key>KP_2: scroll-forw(1,halfpage)

   Warning: Cannot allocate colormap entry for "xxx"
          This comes from the X library. Modern xterm uses the default
          color map. What this means is that if your X server has
          insufficient space to store color information for more than one
          color map, other applications which could use other color maps
          may conflict with xterm. In practice, that is 256 unique colors
          on the screen at a time—not enough for a fancy background or an
          application such as Netscape.

          During resource initialization, xterm attempts to allocate an
          entry from the color map for each color which it might use. If
          there are not enough free slots in the color map, you will see a
          "Cannot allocate" message for each color that xterm failed to
          allocate. Those colors will be rendered in the foreground color,
          making full-screen color applications such as dialog unreadable.

          This problem is alleviated with patch 129, which modified xterm
          to delay the most color allocation until the colors are first
          needed. If a color is never needed (xterm allocates 20 colors in
          this manner), that reduces the number of slots in the color map
          that are needed. Even with this improvement, xterm must still
          allocate 4 colors during initialization to determine how to
          display the cursor. If none of those colors can be allocated,
          xterm reverts to monochrome.

Known Bugs in XTerm and Look–alikes

   These are the known bugs (or limitations) in modern xterm. They are
   also present in the other versions based on the X Consortium sources
   (color_xterm, ansi_xterm, kterm).

   Note that of the emulators that support color, some do not support bce
   (back color erase). The bce capability is also called the "new color
   model", though it has been implemented in the IBM PC for quite a while.
   Technically, not implementing bce (or allowing the choice between it
   and its complement) is not a bug, since few hardware terminals (with
   good reason) implemented this feature.
     * cut/paste does not select tabs; instead spaces are selected. This
       is because the selection works from the array of displayed
       characters, on which tab/space conversion has already been
       performed.
     * does not implement the autorepeat feature of VTxxx terminals.

  X11R6.3 XTerm

   The X Consortium version of xterm (and versions based on it) has
   additional bugs not in modern xterm:
     * the program must be run with fixed (nonproportional) fonts.
     * the home and end keys do not generate usable escape sequences, due
       to an indexing error. (Note that it is possible to work around this
       using the VT100 translations resource, but usually this is not
       done).
     * the Main Options menu is improperly constructed, due to incorrect
       indices after removing the logging toggle. This makes the list of
       signals off by one.
     * very large screens (e.g., by using nil2 for a font) cause core
       dumps because the program uses a fixed array (200 lines) for
       adjusting pointers.
     * certain types of key translations cause a core dump because the
       program does not check the event class before attempting to use
       events.

   (These bugs are also present in the X11R5 version).

   Update 2004/04/08:
   Complicating this discussion is the "X.Org" xterm (from 2004). That is
   the XFree86 xterm from XFree86 CVS with all visible "xfree86" strings
   changed to "X.Org" or "xorg", depending on the use. For example the
   "xterm-xfree86" terminfo entry becomes "xterm-xorg". The change history
   for the related CVS for X.Org shows this. Similarly, the release notes
   for X11R6.7 included my notes for XFree86 4.4.

   As of 2009, it was apparent that "X.Org" xterm had died a natural
   death, since none of the people who created it had any likelihood of
   maintaining it. Instead, X.Org defers to my version of xterm.

   Reviewing in 2014, the major vendors have been using modern xterm
   (different patch levels) for some time. However, there are
   documentation problems with AIX, beyond what is noted here:
     * AIX provides a copy of luit, and a corresponding manpage—which
       omits the sections on security, bugs and attribution.
     * The xterm manpage provided with AIX says this is X11R6 xterm “with
       no functional enhancements.” Comparing releases X11R5, X11R6.1,
       X11R6.3 against the AIX page, it matches X11R6.1 (December 1995).
       That is, it includes the text of the X11R6.1 xterm manpage plus the
       control sequences document—again omitting the security, bugs and
       attribution sections from each.

   The other vendors provide documentation which is more up-to-date.

  COLOR_XTERM download

   This is based on the X Consortium X11R5 source, with the same bugs.
     * implements non-bce color model
     * moving the cursor is reported to leave trails of incorrect color
     * clearing the screen resets colors (arguably this is a limitation).

   Not exactly a bug, but it does not build on Linux with X11R6.3

  ANSI_XTERM download

   This is based on the X Consortium source, with the same bugs.
     * implements non-bce color model
     * fails vttest by not rendering reverse-video screen

  CXTERM download

   CXterm stands for "Chinese Xterm". This is based on the X Consortium
   source.

  DTTERM

   This is distributed with CDE. It implements more of the DEC VT220 than
   the X Consortium xterm, and also adds controls to manipulate the window
   and icon.
     * implements non-bce color model
     * fails vttest by clearing its background to solid white rather than
       preserving its sense in response to ED.
     * under some circumstances, scrolling margins are not recognized. For
       instance, running vile which uses scrolling margins, we see text
       overwriting the status line.

  EMU 1.3 download

   This is not based on the X Consortium source. The authors state that it
   implements VT220 emulation. It is in need of maintenance, since it
   builds with some problems to produce an executable that (on Linux and
   SunOS) does not handle the carriage return and newline translations
   properly. So I am unable to run vttest on this emulator.

  ETERM link

   Eterm was based on rxvt, though the appearance differs. The terminal
   emulation capabilities appear similar, though I am not able to run the
   full suite of tests in vttest with this emulator (the core dump noted
   for rxvt, as well as hanging while awaiting response from one or more
   control sequences). Oddly, it appears that neither Eterm nor rxvt
   implement CPR (cursor position report). Finally, it reserves F1
   (function-key) for a popup menu. This applies to versions of Eterm
   through 0.9.

  GNOME TERMINAL link

   Unless specifically mentioned, GNOME Terminal and VTE's issues
   generally accumulate, with occasional veering off with skin-deep
   "rewrites". Each sighting provides a new episode.

   Starting in 1999 —

   GNOME Terminal is developed separately from both xterm and rxvt, and
   was originally based on the zvt (zterm) widget. Like kvt), it appears
   to have been developed imitating other terminal emulators (Linux
   console and xterm) rather than strictly emulating a VT102. The
   documentation is fragmentary (with a comment suggesting that the author
   does not know where to find relevant information), and the program
   fares badly with vttest. Beginning with late 1999, reports indicate
   that it does not properly parse ANSI control sequences: the vim editor
   is using xterm's vt220-style "Send Device Attributes" (Secondary DA)
   control sequence to obtain the terminal emulator's version. That is, it
   sends

\E[>c

   expecting a response such as

\E[>0;138;0c

   for vt100. The bug report indicates that the "c" sent by vim is echoed
   rather than interpreted by the emulator.

   But it suffices for vi.

   Moving on to 2001 —

   A more recent GNOME Terminal uses the VTE widget. I observed version
   1.4.0.4 in late 2001, which mentioned it in the credits (although VTE
   0.1's ChangeLog mentions no date before February 2002). It does not
   implement a complete vt102: it was missing several features which can
   be demonstrated in vttest). Most of the bugs in the Device Attributes
   responses remain, but it works a little better with vim. However, there
   are problems with the alternate screen that show up with vim. Again,
   these can be demonstrated with vttest (menu 11.6.3 in the 20011130
   snapshot).

   Moving on to 2002 —

   Rather than evolving from zvt, VTE is largely a new work. It does
   credit zvt in one place. However, its source code uses xterm's source
   code as a resource, accounting for odd (often incomplete) chunks.
   Reviewing 0.9.0 (September 2002):
     * the termcap file. The last comment in the file is copied from
       xterm's source. The content of course is generated from ncurses
       with a small number of changes.
     * the parser src/vte.c —a 14,125 line file. For example, the chunks
       related to DEC VT220 keyboard queries and DEC private modes contain
       comments copied from xterm's source code.

   Jumping to 2010 —

   Later versions of VTE incorporate more features (and comments, symbol
   names, etc), from xterm's source. In some instances, the copied
   features were disabled by Red Hat's package for xterm. Here is a
   related bug report, for key bindings.

   The documentation for GNOME Terminal asserts:

     GNOME Terminal emulates the xterm application developed by the X
     Consortium. In turn, the xterm application emulates the DEC VT102
     terminal and also supports the DEC VT220 escape sequences. An escape
     sequence is a series of characters that starts with the Esc
     character. GNOME Terminal accepts all of the escape sequences that
     the VT102 and VT220 terminals use for functions such as to position
     the cursor and to clear the screen.

   That sounds fine, except that it is both inaccurate and misleading:

   inaccurate
          combining the "X Consortium" and "DEC VT220", for example, since
          that was done after the demise of said organization.

          It emulates a subset of VT100, lacks support for most of the
          VT220 control sequences (including some used for positioning the
          cursor) that are not recognized by a VT100.

          Even in the subset which it emulates, GNOME Terminal has bugs.
          Many of these are easy to demonstrate with vttest.

   misleading
          as noted in Xterm Control Sequences, xterm (mostly after "X
          Consortium") supports control sequences which are not
          VT100/VT220. GNOME Terminal implements many of these, but not
          all.

   Perhaps that was unintentional – GNOME developers did not appear to
   document what their program does outside of that remark. However, an
   inspection of the changelog for libvte (VTE) does show that most of the
   borrowing from xterm is cited in an oblique manner – not once
   mentioning XFree86 for example, leaving the impression (as indicated by
   "X Consortium") that all of the work on xterm was done before
   development of GNOME Terminal commenced.

   Most of this observation was documented between 2000 and 2007. Other
   than maintenance, development of GNOME Terminal appeared to have paused
   in 2005. As of 2009, its maintainer was (of the development team), the
   least knowledgeable about terminal emulation. So there was no progress
   on the large number of bug reports related to xterm-compatibility.

   Revisiting in 2018 —

   Regarding documentation, the situation is not as good as reported
   earlier. The problematic documentation was not even part of the
   "official" GNOME Terminal, but was an add-on by a Debian developer,
   adapted from GNOME Terminal's online help. The developer's relationship
   was mentioned in a Debian bug report:

   #127622: ncurses-term: terminfo entry for gnome-terminal swaps
   Backspace/Delete:

>> "TD" == Thomas Dickey <dickey@herndon4.his.com> writes:

> On Sun, Jan 06, 2002 at 06:13:30PM +0100, Christian Marillat wrote:

[...]

>> The upstream author should consider ours Debian changes has official
>> changes ?

> sure - get gnome-terminal's author to make the changes.  (I generally
> don't add customizations to ncurses' terminfo unless I see them incorporated
> intact by more than one other source).

Sorry to say that, but upstream don't care about my patches. I've
forwarded patches since one year, and these patches has never been
included by upstream. Upstream sayd "commited", but I never seen any
changes.

Christian

   The manual page provided as an attachment to GNOME #311565 identifies
   the author. However, four years later there is still no manpage for
   GNOME Terminal. GNOME #701691 mentions this in conjunction with GNOME
   Terminal's incompatible behavior versus other terminals for the “-e”
   option:

 Christian Persch 2013-06-06 11:10:43 UTC

This works as designed. Note that both -x and -e are deprecated; the only suppor
ted way to pass the arguments is after -- like this:

$ gnome-terminal -- emacs file

   and

 Christian Persch 2013-06-06 16:02:54 UTC

There are no docs for the gnome-terminal command line options.

   Admittedly, GNOME Terminal has some documentation, in its online help
   pages. As mentioned, the misleading comments about X Consortium came
   from that material, which remained for more than ten years before being
   revised early in 2013. Here are a few links for that process:
     * help: update introduction.page (2013-01-10)
     * help: review (2013-01-09)
     * help: modified help in accordance with last review (2013-01-09)
     * help: write instroduction.page (2013-01-08)
     * help: start rewrite in Mallard (2013-01-08)

   The document editors removed this statement

     Run any application that is designed to run on VT102, VT220, and
     xterm terminals

   as well as the extended comment about the X Consortium, and replaced it
   with a less specific statement.

     Terminal is a terminal emulator application for accessing a UNIX
     shell environment which can be used to run programs available on
     your system.

     Terminal supports escape sequences that control cursor position and
     colors.

   The assertion about GNOME-Terminal's support for “any” persists in its
   package description in Debian as of 2018:

     * Access a UNIX shell in the GNOME environment.
     * Run any application that is designed to run on VT102, VT220, and
       xterm terminals.

   Whether the revised manual is improved or even helpful is debatable.
   For instance, it tells the reader how to turn the scrollbar on and off
   (using a dialog, of course). But for command-line options, it can print
   only about 45 lines of option names and short (less than 10 words)
   descriptions for each if one types

gnome-terminal --help-all

   Other programs do the equivalent. In a quick check using Debian 8:
     * 85 lines for konsole
     * 120 lines for xterm patch #331
     * 122 lines for mlterm
     * 140 lines for urxvt

   Bug #311565 was (writing in 2018) more than four years ago, but still
   there is no manual page, for either the command-line options or the
   control sequences which it supports.

  Notes on VTE

   VTE is used by developers who provide a facade (also referred to as a
   “skin”) for simple desktop-oriented terminal emulation. This page gives
   a number of examples with sizes for the skins. The actual program size
   is far larger in each case, making the size of the skin irrelevant.

   For more than ten years, VTE's README file asserted

     VTE supports Unicode and character set conversion, as well as
     emulating any terminal known to the system's terminfo database.

   The latter part of that ("emulating any terminal") was incorrect. It
   did have the ability to work with the standard function-key definitions
   which can be defined in a terminfo description. That feature was
   discarded in 2014.

   Notes from 2010 —

   Some of the function-key logic was adapted from xterm; generally
   refactoring the xterm source-code to make it appear different. In
   places however (naming conventions and comments), there was some
   verbatim copying. The same observation can be made of "character set
   conversion". None of that is reflected in VTE's git-log.

   As an aside, the credits in GNOME Terminal's "About" box also are
   inaccurate. For several years (according to its change-log), most of
   the work on VTE (the principal part of the program) was done by Nalin
   Dahyabhai.

   xterm on the other hand, can be told with the tcapFunctionKeys resource
   setting to use a more complete subset, based on the ncurses extended
   terminal descriptions. However, terminal descriptions describe only one
   particular configuration of a terminal. Even xterm's terminfo/termcap
   descriptions do not cover the (literally) thousands of keyboard
   combinations which are available via its resource settings.

   Outside of function-keys, VTE provided no ability to emulate “any
   terminal”. A casual glance at its source code revealed the following:
     * no support for VT220-style protected areas.
     * inconsistent support for modifier keys (the subject of several bug
       reports misdirected toward ncurses).
     * only a subset of the standard terminfo/termcap properties is used
       (5/36 booleans, 3/33 numbers, 125/242 strings other than
       function-keys).
     * a pervasive assumption that the terminal is something like xterm,
       e.g., to provide hardcoded behavior where termcap might describe
       something different.
     * it uses termcap to retrieve data, rather than providing a choice
       between terminfo/termcap, opening up the problem of using an
       obsolete database.
     * using termcap also means that it has no guidance for following
       features which are absent or have limited-functionality compared to
       terminfo, such as setting video attributes, colors, etc.

   For instance, VTE cannot emulate dtterm, because of differences in
   color behavior. In fact, VTE does not use any of the termcap data to
   support its interpretation of color control sequences.

   After 2014 —

   Until 2014, VTE used a termcap file, with its own reader, presumably
   under the impression that could be used to describe “any terminal”
   (although it was fairly well known that terminals could support escape
   sequences not found in any terminal description). As a separate file,
   the termcap was a nuisance, whether it was bundled with VTE (and
   inaccessible to users) or not. The developers tried it both ways.

   One recurring problem was that VTE's termcap did not match xterm's
   function-keys. Even when VTE's developers modified the termcap to match
   as well as the termcap could, the match was still incomplete. None of
   the modified keys were correct, since none of those are described by
   termcap. That meant that a control modifier with a cursor-key or
   function key was likely to be misread by programs running in VTE.

   Finally in 2014, the VTE developers decided to change it. First, one
   decided to adapt a chunk of source-code from ncurses, perhaps thinking
   that was the way to get a better reader. That did not work well, and
   finally they discarded the whole feature, hardcoding the behavior to
   match xterm's default configuration.

   Here are bug reports which give the story:
     * #600659 – Home/End generate wrong control sequences.
Escape sequences of the "default" kbd mode should be okay now.

Removal of non-default kbd modes is continued in bug 730137.

     * #169295 – builtin termcap parser not needed.
all: Use terminfo instead of termcap

     * #730137 – Drop (or fix) nondefault fkey modes.
       Since addressing bug 600659, VTE's default mode pretty accurately
       matches XTerm. VT220 is okay-ish, Legacy is so-so, HP and Sun are
       quite broken.
     * #728900 – use terminfo instead of termcap.
       Do we want to rely in term{cap,info} *at all*? So far vte has used
       hardwired sequences most of the time. Even if we clean up
       everything and drop all fkey modes except the default (request: bug
       600659 comment 73) we'd need to keep hardwired sequences for
       numerous reasons. E.g. Home/End should generate ^[[H/^[[F which are
       not present in terminfo. Application cursor keys and application
       keypad mode alter some sequences, with AFAICT no terminfo support
       whatsoever. F1..F4 completely change their sequences when a
       modifier is pressed, again probably no support for it in terminfo.
       Terminfo is just able to encode the complexity (app keypad mode,
       app cursor mode, modifiers, numlock) we need. Wouldn't life be much
       simpler with just hardwired xterm-compatible sequences? (With
       probably a way to override them from config file or dconf for
       experts.)

   As a minor improvement, those changes removed some of the code whose
   origin was cut/paste from xterm. But that does not mean that the VTE
   developers stopped that practice. For instance, a change in late 2017
   here reminded me to check what VTE does when saving/restoring the
   cursor position. It turns out that it does something similar, because
   (see #731205 and #741193) the developer studied xterm's source-code and
   imitated it (see source changes and followup fixes). There's a quirk in
   the resulting program (it pays attention to send/receive and insert
   modes, which are unrelated, while also missing the handling of wrap
   state), but if the developer had read the documentation (DEC's
   manuals), that detail would be missing. In reviewing the documentation,
   I noticed a different aspect which might be used to improve xterm, and
   ultimately appear in VTE (or perhaps not, since it is in an area poorly
   supported by VTE, i.e., the bug which was reported).

   VTE developers do more than copy from xterm, of course. There are other
   programs (such as Konsole and Terminal.app) which get similar
   treatment. Because they tend to copy from others rather than doing
   their own solutions, they have not acquired the experience to see why
   features were added or modified (or removed), just that it is there.
   For instance:
     * In a recent rewrite (early 2018), they introduced a skeleton of
       code from Paul Williams' sample parser. However, that is only a
       skeleton. For the flesh – the usual approach (see above).
       Two thirds of the functions listed in the skeleton are no-ops (not
       implemented). Some of those listed as implemented do not work (see
       vttest screenshot).
       Oddly enough, the developers decided to make the program claim that
       it is a VT525, though the skeleton demonstrates that it lacks
       almost all of features provided by the corresponding hardware
       terminal. In October 2018, the listing shows mostly a subset of
       VT100, with some (longstanding) features adapted from xterm, and a
       few inspired by ECMA-48.
     * The latter requires some comment: xterm's control-sequences
       document has mentioned ISO-6429 and ECMA-48 since its earliest
       version. VTE's developers used that as a reference (see bug
       reports) along with xterm's source-code rather than ECMA-48 or
       DEC's manuals until around the end of 2016.
     * They did (eventually) read documentation referred to by xterm's
       documentation. But that took a while, and they began copying from
       those sources before understanding the tradeoffs in those. Late in
       2016, they started copying features mentioned in ECMA-48. The
       motivation for that appears to be (unsurprisingly) copying from yet
       another source, e.g., kitty (yet another copyist: see alacritty,
       but also see this).
     * Introducing those ECMA-48 features caused additional failures for
       VTE versus vttest, which the VTE developers solved by making a copy
       of vttest, to “fix” the bug. The problematic feature dealt with
       clearing tab-stops (selection 2).
       ECMA-48 specifies the active line in selection 2. For an
       explanation of the term, see ECMA-48 section 6.1.5 Relationship
       between active data position and active presentation position. This
       is distinct from the feature which DEC's terminals supported.
       The VT520 manual is explicit in this case (only selections 0 and 3
       are supported). Per Lindberg's 1985 test demonstrated that the
       unsupported selection 2 was ignored in a VT100.
     * The VT520 did not support the other selection (2) because that
       would have been used to support bi-directional text. There is no
       point in having two differently-worded descriptions of the same
       identical feature.
       At the time the VTE developers copied the feature, they had not
       begun to develop support bi-directional text (see for example
       #321490 (vtebidi) and #767529 (vteemoji).
       At this writing (two years later), the developers are talking about
       working on that. The tab-clear operation is still identical in VTE
       for both selections 2 and 3, and does not implement any of the
       features from ECMA-48 not in a DEC terminal.

   Other problems with VTE —

   These are a few of the interesting bugs found in VTE (or GNOME
   Terminal) during 2017:
     * system crash due to running out of memory
       while running ncurses sample programs dots and picsmap.
     * failure to open a remote connection, noticed
       while gathering data for a discussion of scrolling performance.

   Other uses of VTE —

   Because of GNOME Terminal's reputation for excessive code bloat,
   developers of every other program based on VTE advertise their version
   as reduced memory usage, faster startup, etc. Here are a few of the
   available ones:
     * osso-xterm link
       Its home page refers to "at least two versions". I recall seeing an
       older version which was apparently not based on VTE. There did not
       appear to be any relevant page (as of 2009) for that version.
     * roxterm link
     * XFCE Terminal link

  MULTI GNOME TERMINAL (MGT) link

   Of particular note, MGT 1.4.0 announcement claims that it works
   properly for all of vttest)'s tests. On the positive side, it does do
   VT52 emulation, but (reading the source code did not help) it
   apparently does not really do VT220 from vttest's perspective.

  HANTERM download

   HanTerm stands for "Hangul term" (Korean). This is based on the XFree86
   source.

  KONSOLE link

   More than just a rewrite of kvt into C++. But there are several
   incompatibilities between konsole (noted with version 1.0.2 in late
   2001) and xterm:
     * none of the selections of keyboard mappings match the actual
       behavior of xterm (a few come close, but do so by matching the
       terminfo descriptions rather than the programs). In particular, the
       application keypad does not send vt100-style escapes.
     * vttest) demonstrates that konsole does not properly ignore escape
       sequences to switch character sets that it does not support. Also,
       the developers of konsole did use an old version of vttest, but
       that was to add a bogus Device Attributes response (claimed to be
       for "vt220", but not corresponding to any that DEC produced). They
       do not use the newer version of vttest (which was available more
       than a year before development of konsole began).
     * konsole implements several features from XFree86 xterm, but some
       are done incorrectly. In particular, the private setmode 1049 does
       not save and restore the cursor, causing the cursor to be in
       unexpected locations after exiting a fullscreen application such as
       vi.

   The problems with setmode 1049 were fixed after some time; other issues
   linger on.

   Like GNOME Terminal, konsole's documentation is incomplete and
   inaccurate. This gem from its handbook illustrates the problem:

     After a decade, Konsole is the first rewrite from the ground up.
     While xterm has definitely been hacked to death (its README begins
     with the words Abandon All Hope, Ye Who Enter Here), Konsole offers
     a fresh start using contemporary technologies and understanding of
     X.

   The problem:
     * the remark was apparently written in 1997. It was inaccurate at
       that time, since it disregards the earlier xvt/rxvt applications.
       Limiting it only to a plain statement that konsole was a rewrite of
       kvt would have been more accurate. Lacking that context, we find
       nonfactual articles such as this on the net.
     * for those lacking a proper education, the README was apparently
       intended to be a humorous reference to Dante's Inferno.
     * reading konsole's source code and considering "hacked to death" can
       provide some occasion for humor. Enjoy.

  KTERM download

   KTerm stands for "Kanji term" (Japanese). This is based on the X
   Consortium source, with the same bugs (though the list of original
   authors has been removed; the modifications that comprise kterm is
   relatively small).
     * implements non-bce color model
     * implements status line, but uses non-DEC escape sequences for this.

   There is a variation of xvt (ancestor of rxvt) originally known as kvt
   bundled with KDE which may be referred to as "kterm", but I do not find
   it interesting, other than to comment that it was a poor choice of
   name.

  MLTERM

   Mlterm is not based on xterm or rxvt source, though it implements many
   of their features. It does fairly well with vttest, except for some odd
   misbehavior in operations that save/restore the cursor position.

  MTERM

   There are a few variants of this: the xterm bundled with some Motif
   clients is more common. More interesting, however is one (not Motif),
   attributed to "Der Mouse".

(mouse@Lightning.McRCIM.McGill.EDU) Available:
larry.mcrcim.mcgill.edu (132.206.1.1) in
/X/mterm.src/mterm.ball-o-wax.

   I saw only an incomplete version of this while it was advertised in the
   mid-90's. It is available by email from <mouse@Rodents.Montreal.QC.CA>.
   or via ftp. This is not a patched version of xterm, though it was
   apparently written, like rxvt, to emulate vt100's. While it does have
   some interesting features (such as blinking characters), overall it
   does not do as well with vttest as the more widely known emulators.

  MXTERM

   There are several variants on this: xterm adapted for Motif libraries.
   I have seen none that work properly:
     * MXTERM: a motif Xterm with character attributes color rendered I've
       noticed this one only recently. It is a reworking of the earlier
       patches for color_xterm (credited to Erik Fortune at SGI) and the
       Motif widgets (apparently first done by Ivan M. Hajadi at SGI in
       1991, but credited in this release to Mahesh Neelakanta, for Motif
       1.2.4).
     * ANSI Xterm with Motif Scrollbar Usually seen as the
       ansi-xterm-R6-motif-sb patch, I used this as the starting point for
       changes to my #82 patch of xterm in August 1998.
       The original patch changes only the scrollbars to Motif, leaving
       the popup menus in Athena widgets. That was not what I wanted. My
       motivation for using Motif is not for performance or esthetics, of
       course, but to make it simpler to build on hosts that have no
       Athena widgets installed.
       I set those changes aside, having found (the hard way) that the
       Motif library has hardcoded behavior regarding the control
       right-mouse button. According to the O'Reilly book on Motif
       programming (volume 6), it does a server grab when processing
       menus. Making the menus behave just as in the Athena widgets can
       cause the X server to hang. (I was able to do this with both
       Lesstif and Motif libraries). Given that, I decided to restructure
       the menus entirely, making a toolbar which could support at
       compile-time either widget set.
     * mxterm This is a different reworking of the Motif widget patch,
       using a 1993 version (ignoring the more recent 1994 patches noted
       above). However, it appears to have the same technical defect that
       I noted above.

  NXTERM

   Distributed with Redhat Linux 5.2, it is a repackaging of
   xterm-sb_right-ansi, to use the Xaw3d widget set. This is based on the
   X Consortium X11R6 source, with the same bugs.
     * implements non-bce color model
     * does not implement SGR 39 and SGR 49, all attributes are reset when
       changing colors.
     * popup menus do not appear to work.

   Starting with Redhat 6.0, nxterm is the XFree86 3.3.6 xterm.
   Unfortunately Redhat neglected to update their termcap for nxterm to
   match the program.

  RXVT link

   Rxvt's manual page states the following unqualified comment:

     rxvt, version 2.6.2, is a colour vt102 terminal emulator intended as
     an xterm(1) replacement for users who do not require features such
     as Tektronix 4014 emulation and toolkit-style configurability. As a
     result, rxvt uses much less swap space -- a significant advantage on
     a machine serving many X sessions.

   How much is much less? Perhaps not as much as one would think from
   reading that. The Tektronix emulation in xterm (which has been optional
   since late 1997) accounts for about 25kb of the code.

   The toolkit-style configurability glibly referenced is the ability to
   redefine keys on the keyboard without recompiling the program, i.e.,
   the translations resource. It also is the way mouse events and other
   actions are passed to xterm.

   The toolkit-style configurability accounts for about 300kb, which does
   add up if you happen to be running 50 xterm processes (i.e., about
   10Mb).

   This comment was topical in December 2001:

     Compared with something like GNOME Terminal, which takes 2-3 times,
     or KDE konsole, which takes 15-20 times as much memory to run, xterm
     and rxvt memory requirements are indistinguishable to the normal
     user.

   In June 2010, the numbers had changed somewhat. Here is a table showing
   the total application and library sizes needed for each of the terminal
   emulators on my development machine. All sizes are in kb (1024 bytes).

        program       base size total size libraries
   aterm              127       10763      45
   color_xterm        142       3647       13
   Eterm              1         5126       19
   fbiterm            6         2424       8
   gnome-terminal     292       14587      51
   hpterm             146       14386      31
   konsole            2         39815      71
   kterm              226       4194       17
   mlterm             316       6606       27
   mrxvt              298       4515       19
   multi-aterm        144       2821       7
   pterm              405       12817      42
   rxvt 2.6.4         108       2725       6
   rxvt 2.7.10        152       2829       7
   rxvt-unicode       1259      13641      49
   terminal.app       211       15274      29
   wterm              110       2922       11
   xfce4-terminal     148       14059      48
   xgterm             953       4602       14
   xhpterm            130       2748       6
   xiterm             12        3762       16
   xterm (everything) 346       5484       24
   xterm (minimal)    186       4123       15
   xterm-r5           135       4164       11
   xterm-r6           140       4169       11

   Counting the libraries is appropriate, since some programs such as
   xiterm and the VTE-based programs are implemented in libraries.

   These comments apply to versions of rxvt through 2.21:
     * clearing the screen resets colors
     * does not have a delete key
     * the implementation of ech (erase characters) does not follow DEC
       VT220 (also ISO 6429), causing applications using this function to
       misbehave.

   A newer version (upgraded to an beta as of 2.6.PRE3, however, since it
   no longer dumps core in vttest) is reported to fix the ech bug.
   However, it is less VT100-compatible than the earlier versions such as
   2.21b because it does not render reverse video (DECSCNM) properly. All
   versions do not update the screen frequently enough, making animation
   ineffective. See vttest, tests 1 and 2.

   One longstanding issue with rxvt impacts use of xterm. While rxvt does
   not use the X Toolkit (and corresponding X resource matching), it does
   read your .Xdefaults and app-defaults files to extract resource
   settings. That in itself would not be a problem. However, since rxvt
   also looks for resources in the XTerm class (a parasitic relationship
   like setting $TERM to "xterm" based on the presumption that it is a
   nuisance to install its configuration files), there have been several
   occasions on which xterm's app-defaults files have been modified to
   accommodate rxvt's variant usage.

   That comment applies mainly to the resource patterns. However, even
   when the pattern is reasonably unambiguous, but overbroad, the results
   can be conflicting. For example, some versions of rxvt may accept a
   font resource which does not match the XLFD pattern. It accepts a
   prefix of "xft:". This feature (apparently introduced by konsole) tells
   rxvt to interpret the remainder of the string as a TrueType (Xft) font
   rather than a bitmap font. xterm uses the faceName resource for these
   values.

  st link

   Rxvt revisited, this program originally depended only on the X11
   library. Since then, it has grown a lot, though the project page does
   not mention it. As of January 2013, it was in heavy development, and
   (according to comments on its developer's list) growing steadily as the
   developers implemented useful features adapted from xterm.

   For instance, in 2013, the size counting libraries for st 0.3 on my
   Debian testing machine was on a par with rxvt (and half that of xterm,
   which uses the X Toolkit library). Revisiting it late in 2015, it had
   left rxvt behind and was nearly as large as xterm. Here are the sizes
   which I found in Fedora 22:

   LDD-Size    Program
    3452986 rxvt
   6060960  st
    6771039 mrxvt
   7785780  xterm
   15060195 urxvt
   20934874 lxterminal
   21089908 lilyterm
   21358156 xfce4-terminal
   25738679 roxterm
   31195794 gnome-terminal
   32780414 terminology
   87813125 konsole

   By the way, the project page quotes the README file from xterm's
   sources, omitting my editorial comment at the top noting that the
   paraphrase of the opening from Dante's Inferno dated from 1991, and
   pointing to this FAQ to provide better context.

  XGTERM link

   It has some features which are also in color_xterm:(non-bce ANSI color,
   colorBD and colorUL resources, cursor warping, etc. The main feature is
   its Tektronix graphics emulation, which is the main reason for this
   particular program. Neither program has a change-log, so it is not easy
   to say which influenced the other.

   That is from reading the source code. However testing under Debian
   Linux, something is wrong with the resource processing (neither popup
   menus nor colors work).

  XITERM link

   This appears to be rxvt 2.20, lightly reformatted, with a few ifdef's
   changed.

   That is, it was. The name was later appropriated by a different
   program, which also uses the name iterm. Like gnome-terminal, iterm
   aims to be an xterm-emulator rather than a VT102- or VT220-emulator.

   An earlier attempt by the same author (the "CSI-xterm") incorporated in
   2002 some of the changes I made for XFree86 xterm via cut and paste
   (but does not mention this in its README). The "borrowed" changes
   comprised about 10% of the patch provided for X11R6.5.1, summarized
   here:

xterm-6.5.1-i18n-0.7.patch.gz
 Imakefile     |   25 +
 RELNOTES-I18N |  104 ++++++
 XTerm.ad      |    1
 button.c      |  155 ++++++++-
 charproc.c    |  979 ++++++++++++++++++++++++++++++++++++++++++++++++++++------
 data.c        |    6
 data.h        |    4
 error.h       |    8
 fontutils.c   |   78 ++++
 fontutils.h   |    8
 input.c       |   11
 main.c        |   40 +-
 main.h        |    1
 misc.c        |   46 ++
 ptyx.h        |  156 ++++++++-
 screen.c      |  513 +++++++++++++++++++++++++++---
 scrollbar.c   |   36 +-
 util.c        |  218 +++++++++++-
 18 files changed, 2183 insertions(+), 206 deletions(-)

   This patch was said to be the basis for Solaris 10 xterm, and was
   briefly referred to as the Solaris "color xterm". It did not use the
   bce color model however, and Sun provided no terminal description for
   it.

   Back to iterm: the author's README in the patch used the same
   terminology as in the later work, demonstrating their relationship:

 This is a patch for the xterm of X11 release 6.5.1 to fix its
internationalization defects. This patch enables xterm to handle
whatever the character set encodings and scripts support underlining
operating system supports via the technology called CSI(Code Set
Independence) and XOM(X Output Method). Traditionally, several
X terminal emulators which are hard-wired to specific languages and
encodings were introduced to support local language requirements, such
as kterm, hanterm, cxterm, UTF-8 xterm and so on. This  truly
internationalized terminal emulator supersedes the needs of those
multiple locale specific terminalemulators.

   The key to understanding the "code set independence" is that the author
   intended to treat existing character encodings on an equal basis with
   Unicode and UTF-8. Some of that is reflected in the Solaris
   International Language Environments Guide, but in explaining how this
   is done, the documentation is weak, lacking detail.

   Either version of iterm has similar problems running vttest.

How do I build XTerm?

   Building a copy of xterm is simple, provided that you have a
   development configuration for X11:
     * Header files and libraries. If you do not have the header files
       (usually under /usr/include/X11) for your system, you are better
       off building the libraries yourself. Xterm can be built with either
       X11R5 or X11R6 libraries; however X11R6 requires much more data to
       be installed before xterm will run. Xterm uses the Xaw library for
       popup menus.
     * imake and xmkmf. These utilities produce a Makefile from the
       Imakefile. They are not essential, but useful, particularly on
       systems with unusual configurations.

   If you have a working xmkmf script (or correctly configured imake
   utility), all you need to do is type

xmkmf
make

   I have written a configure script for xterm which can use imake (or
   xmkmf) to generate a Makefile from the Makefile.in. Or it can do
   without imake entirely. I have restructured xterm to eliminate most
   hardcoded #ifdef's, replacing them with definitions that can be derived
   with the configuration script. The configure script is more flexible
   than xmkmf, since it allows you to enable or disable a variety of
   features. Type

configure --help

   to get a list of options.

   Though I have replaced most hardcoded ifdef's with autoconfigured
   values, it will still continue to build properly with the imake
   environment.

   However, I usually build xterm using the configure script. By default,
   it looks for imake and will use it to help with a few places where a
   reliable configure check cannot be created. One of these (see Why
   doesn't the scrollbar work?) can be a problem.

   As with all of my projects, I routinely check for strict compiler
   warnings. For gcc, that is done with the "gcc-stricter" script which
   you can find here. The X libraries have a longstanding issue which has
   been ignored so far (as of mid-2012). To work around this (and get
   useful warnings), I apply this patch:

--- Intrinsic.h.orig    2009-08-25 13:22:15.000000000 -0400
+++ Intrinsic.h 2009-12-06 09:48:39.000000000 -0500
@@ -66,7 +66,11 @@

 #define XtSpecificationRelease 6

+#ifdef _CONST_X_STRING
+typedef const char *String;
+#else
 typedef char *String;
+#endif

 /* We do this in order to get "const" declarations to work right.  We
  * use _XtString instead of String so that C++ applications can
--- Xresource.h.orig    2009-07-19 14:43:21.000000000 -0400
+++ Xresource.h 2009-12-06 10:11:19.000000000 -0500
@@ -338,8 +338,8 @@
 } XrmOptionKind;

 typedef struct {
-    char           *option;        /* Option abbreviation in argv          */
-    char           *specifier;     /* Resource specifier                   */
+    _Xconst char    *option;       /* Option abbreviation in argv          */
+    _Xconst char    *specifier;            /* Resource specifier
    */
     XrmOptionKind   argKind;       /* Which style of option it is          */
     XPointer       value;          /* Value to provide if XrmoptionNoArg   */
 } XrmOptionDescRec, *XrmOptionDescList;

   I made note of it on the Xorg mailing list, but as you can see, there
   was no response.

How do I report bugs?

   You should report bugs to me. I also respond to bug reports in a number
   of bug-tracking systems, though some are less open to searches than
   others. See also:
     * reporting/patching procedures.
     * analyzing problems with configure scripts

Additional Information

   There appears to be no comprehensive source of information on xterm
   better than the documentation which comes with the source code
     * XTerm change log
          + The XTerm Manual
          + XTerm Control Sequences
          + resize – set TERMCAP and terminal settings to current xterm
            window size
          + uxterm – a UTF-8 wrapper for XTerm
          + koi8rxterm – a KOI8-R wrapper for XTerm
          + luit – Locale and ISO 2022 support for Unicode terminals
     * Other Sites
     * Interesting but misleading

    The XTerm Manual

   The command-line options, X resources and similar configurable options
   of xterm are documented in the manual page.

   Here are copies of the file in various forms: html, pdf, ps and text.

    Xterm Control Sequences

   Control sequences, i.e., programming information are in the ctlseqs.ms
   file which I bundle with the program source. (It used to be in the same
   directory in the X distribution, but was moved to a different part of
   the tree long ago). Note that you must format this file with different
   options than a manpage, e.g.,

tbl ctlseqs.ms | nroff -ms >ctlseqs.txt
tbl ctlseqs.ms | groff -ms >ctlseqs.ps

   As a PostScript or PDF file, the individual letters of the control
   sequences are all boxed, for emphasis, but I find the text file equally
   readable.

   Here are copies of the file in various forms: html, pdf, ps and text.

    resize – set TERMCAP and terminal settings to current xterm window size

   resize is useful by itself, but is maintained for historical reasons as
   part of xterm. html, pdf, ps and text.

    uxterm – a UTF-8 wrapper for xterm

   XTerm does not automatically set your locale. It can be told to use
   your locale settings. This is a shell script which sets xterm's
   resources to use UTF-8 encoding, and use UTF-8 fonts. There is a
   similar lxterm script, but it relies upon non-portable applications,
   unlike uxterm.

   Here are copies of uxterm's documentation: html, pdf, ps and text.

   Incidentally, there was a different program named "uxterm" before the
   shell script was added to xterm in mid-2000. Roman Czyborra commented
   in 1998 that it was based on the original X11 xterm source (very
   likely, since "strings" run on the executable shows the xterm actions,
   resources and even the Tek4014 support). There are few references to it
   to provide details: the first appearance was in 1994, and the last was
   Czyborra's page in 1998. For the curious, there is a copy on
   ibiblio.org (no Linux executables, no source, however).

    koi8rxterm – a KOI8-R wrapper for xterm

   As a special case, this wrapper is packaged with xterm to provide
   KOI8-R encoding.

   Here are copies of koi8rxterm's documentation: html, pdf, ps and text.

    luit – Locale and ISO 2022 support for Unicode terminals

   luit also is maintained as part of xterm, since its upstream maintainer
   is inactive, and the ostensible maintainers have more than once
   delivered unusable versions, causing many bug reports to be issued
   against xterm.

  Other Sites

     * I have found Richard Shuford's archive to be invaluable for notes
       on the DEC VT220 and related terminals. This was a webpage but was
       last seen via ftp. I have a snapshot of the ftp site, here:
          + ftp://invisible-island.net/shuford/
          + http://invisible-mirror.net/archives/shuford/
     * Though not available at the time that I was collecting most of my
       notes, VT100.net is also a good source of primary information.
     * As part of my Git exports work in 2016, I made a repository of the
       major X release copies of xterm source. Alan Coopersmith has a more
       extensive repository of the X source, which is also useful although
       it does not cover the full timespan. In my repository, I combined
       the controls-sequences document which was in specs with the
       program:
          + xterm was first released in X10R3, with a manual page in the
            man directory, and program in the xterm directory.
          + The developers (re)organized the directory tree in X11, moving
            some manual pages under the doc tree, others went along with
            the source-code, and moving the programs such as xterm under a
            clients directory.
          + The control-sequences document was first released in X11R4.
          + When making the repository, I overlooked the X10 manual page.
            Git isn't flexible enough to add that later, without
            re-creating the repository.
       I use RCS as a starting point for creating Git repositories because
       it is the simplest way to capture each file's timestamp. Since the
       X developers switched source repositories between X10 and X11, and
       the RCS identifiers were no longer in sequence, I used a script to
       change those identifiers to a form that would not interfere with
       checking the sources into RCS.
       The dates shown are, of course, for the xterm source-code:

          Date     Release     Mine    Alan's
                            old-xterm Program Specs
       2005-12-14 X11R6.9.0 link      n/a     n/a
       2005-01-12 X11R6.8.2 link      n/a     n/a
       2004-08-20 X11R6.8.0 link      n/a     n/a
       2004-04-02 X11R6.7   link      n/a     n/a
       2001-02-09 X11R6.6   link      n/a     n/a
       2000-08-21 X11R6.5.1 link      n/a     n/a
       1998-02-09 X11R6.4   link      n/a     n/a
       1996-12-09 X11R6.3   link      n/a     n/a
       1996-02-02 X11R6.1   link      n/a     n/a
       1995-01-30 X11R6     link      link    link
       1993-11-11 X11R5     link      link    link
       1989-12-23 X11R4     link      link    link
       1988-10-27 X11R3     link      link    n/a
       1988-03-01 X11R2     link      link    n/a
       1987-09-15 X11R1     link      n/a     n/a
       1986-12-25 X10R4     link      n/a     n/a
       1986-05-17 X10R3     link      n/a     n/a

  Interesting but misleading:

     * The ncurses FAQ How do I get color with VT100? discusses a widely
       cited bit of misinformation.
       For instance, this web search gives 3,000 hits in March 2015.
     * Also widely cited, Consistent BackSpace and Delete Configuration
       gives advice regarding backspace and delete keys which is heavily
       biased toward Linux. For instance:
          + the console referred to is the Linux console, which initially
            had as a goal VT220 emulation. Linux never came close to
            meeting that goal, which was abandoned in the late 1990s when
            UTF-8 became more important.
            As part of that, Linux's keyboard was (actually modelled on
            xterm) said to be VT220, and its coding for the backspace key
            sent DEL. In contrast, ncurses' terminal database says kbs for
            the vt220 sends ^H (BS).
          + the guideline uses "newer", "right" and "correct" in the part
            which describes DEL, versus "dirty" and "break", "broken" in
            that addressing BS.
       In addition to bias, the technical remedies are unsuitable for
       generic advice. In particular, the comments about terminfo, xmodmap
       and xterm's translations resource are suitable only for special
       cases because the proposed solutions create problems of their own.
       The page itself was written in 1997, with only minor fixes since
       then. Thus, it does not reflect any of the improvements made to
       xterm. Its lack of relevance does not prevent people from citing
       it. For instance, this page's accepted answer recommends that
       (although neither gives a useful answer to the question). Here are
       a few clues:
          + Debian's current package for ncurses uses the --with-xterm-kbs
            configure option which I added in 2012. Debian also applies
            patches to many of the terminal descriptions, including adding
            a patched copy of xterm's terminfo file to ncurses's terminfo
            file.
            The patched copy is redundant and a source of problems (since
            the two overlap, with slightly different goals regarding PC-
            and VT220-style keyboards). My intent in adding the configure
            option to ncurses was to wean them away from the patch. That
            has not happened yet.
          + tmux is (mostly) a terminfo application. However, it does not
            use the terminal database's kbs value. Rather (referring to
            the source for 1.9a), it uses the termios setting:

             /*
              * Check for backspace key using termios VERASE - the termin
     fo
              * kbs entry is extremely unreliable, so cannot be safely
              * used. termios should have a better idea.
              */
             bspace = tty->tio.c_cc[VERASE];
             if (bspace != _POSIX_VDISABLE && key == bspace)
                     key = KEYC_BSPACE;
            At the same time, tmux sets $TERM to "screen", by default.
            Debian patches that terminal description, too. Applications
            running inside tmux use that terminal description. If instead
            tmux translated the backspace key to match the value from
            erasechar (for the given $TERM), its clients would receive
            consistent information.
            Thus, rather than blaming the user (for a "badly configured"
            xterm), the actual problem is a design flaw in tmux which
            should have been sent to its developers in a bug report.
     * Noted here, someone pointed out an NCDware document describing its
       terminal control sequences.
       Disregarding the title Using VT320 Terminal Emulator Escape
       Sequences, it described some variant of xterm rather than a DEC
       VT320. VT320s for example had no "alternate screen". Nor did it
       have a feature for the "curses (1) fix".
       The NCD documentation (dated December 12, 1997) does not mention
       xterm. A related manual does mention xterm, but only in other
       sections. There are other issues with the manual. For example,
       aixterm (16-color) control sequences are documented as
       "NCD-specific values". NCD did add escape sequences for status line
       (kterm did this as well, according to the 6.2.0 sources dated July
       1996), as well as VT220 national replacement characters (which I
       added early in 1998).
     * Terminal Function Key Escape Codes has good intentions, but falls
       astray in several respects.
       For a different treatment of the same material, see my notes:

     Table of function-keys for XTerm and other Terminal Emulators
       First off, it (like the the documentation for GNOME Terminal)
       misattributes work which I did, crediting the X Consortium:

     This brings me to xterm. xterm has a long history, and the function
     key definitions have changed over time. The original xterm from the
     X Consortium (even before they were absorbed by The Open Group) used
     escape codes based on the VT220, but extended to cover the range
     from F1 to F48. F1 through F12 generated, respectively, codes ^[[11~
     to ^[[15~, ^[[17~ to ^[[21~, ^[[23~, and ^[[24~. Shift-F1 through
     Shift-F12 were used for F13 through F24, and generated codes from
     ^[[11;2~ to ^[[24;2~. Similarly Ctrl-F1 through Ctrl-F12 were used
     for F25 through F36 and generated codes ^[[11;5~ to ^[[24;5~, and
     Ctrl-Shift-F1 through Ctrl-Shift-F12 were used for F37 through F48
     and generated codes ^[[11;6~ to ^[[24;6~. None of the base xterm
     $TERM types on my system correspond to this series of escape codes,
     though you can still get xterm to exhibit the old behavior by
     setting the OldXtermFKeys resource to 'true'.
       Not only that, but the comment (and much of the page) is
       inaccurate. For instance:
          + The X Consortium went out of business late in 1996 (see press
            release from July 1996).
               o The first release of X11R6 was done early in 1996 by X
                 Consortium.
               o I've been working on xterm since before that (see
                 history).
          + The X Consortium xterm only knew about function keys up to
            F20.
               o X11R5 defined only 20 function keys, and xterm used only
                 those since May 1991.
                 X11R6 changes to xterm did not take advantage of
                 additional keys aside from the Insert and Delete on the
                 keypad.
               o Further changes by The Open Group through X11R6.6 made no
                 changes to xterm's handling of special keys.
               o That came in xterm patch #130 (2000/3/1), starting with
                 the SCO function-keys feature.
          + The X Consortium xterm didn't know about using Shift to get
            F13 through F24.
               o I introduced a similar feature (using Control) in patch
                 #51 (1997/9/15) as the sunKeyboard resource.
                 I did this to leave Shift for the VT220 UDK (user-defined
                 keys).
               o rxvt used Shift; the key combination was popular.
               o Alexander V Lukyanov's changes in patch #121 to update
                 the terminal descriptions for these keys took that into
                 account.
          + The X Consortium xterm didn't know about using Control to get
            F25 through F36.
               o Even with X11R6, the last function key was XK_F35.
               o However, since xterm patch #94 (1999/3/27), it accepts
                 modifiers (shift, control, alt) to extend the actual set
                 of keys to generate different escape sequences.
          + The escape sequences described all date from 2002 (xterm patch
            #167).
               o Besides function-keys, there are two other groups of
                 special keys on the keyboard: cursor and editing-keypad.
               o Before then, the "2" and "5" in cursor- and home/end
                 sequences would be first (before the semicolon).
               o By that point, GNOME Terminal and KDE Konsole had copied
                 the earlier behavior, and failed to follow this change.
               o At the time, I preferred the VT220 keyboard (that does
                 not support modified special keys).
               o However, the app-defaults file which I provided with
                 xterm did not set the sunKeyboard resource to do this.
                 Packagers routinely altered the recommended
                 configuration, so this difference was not noticed for a
                 while.
               o In response to a bug report, I switched to the Sun/PC
                 keyboard, using the xterm-pc-fkeys building blocks in
                 ncurses' terminfo description for xterm.
          + The X Consortium xterm had incomplete support for VT100
            keypad.
               o I added a resource sunKeyboard to tell xterm to look at
                 other keyboards to simulate the keypad.
               o To do this, I made F1 through F4 act like the VT100 PF1
                 through PF4.
               o That came in xterm patch #79 (1998/6/28).
               o Not everyone liked that, so I added another resource to
                 allow turning off the change to F1 through F4.
               o Actually OldXtermFKeys is the resource class; the actual
                 resource is oldXtermFKeys.
       By the way, although The Open Group made changes, none of those
       have been incorporated in this version of xterm. That was
       intentional (see discussion). Consequently, the xterm copyright
       makes no mention of The Open Group.

Ongoing/future work

     * soft (downloadable) fonts
     * printer interface
       Done, except for the corresponding support in the VT52 emulation.
       It would be nice to have a dialog to control this.
     * allow alternate libraries for popup-menus and dialogs
       My configure script currently provides tests for the variations of
       Athena widgets (Xaw3D, neXtaw). I intend to make additional changes
       to support Motif scrollbars and menus. Motif requires a different
       style of interface for the menus: binding a popup menu to control
       right mouse may cause the server to hang. As an intermediate step,
       I implemented a toolbar for the Athena widgets. In turn, that works
       well enough except with XFree86 4.x: the Xaw library geometry
       management is broken. (Other implementations of the Athena widgets
       work well enough).
     * popup window that shows hex code for content of a character cell
       and hexadecimal keyboard entry for all Unicode characters (ISO
       14755)
     * correct cut&paste of TAB character
