runtime/doc/gui_x11.txt

*gui_x11.txt*   For Vim version 7.0aa.  Last change: 2004 Jul 02


		  VIM REFERENCE MANUAL    by Bram Moolenaar


Vim's Graphical User Interface				*gui-x11* *GUI-X11*
							*Athena* *Motif*
1. Starting the X11 GUI		|gui-x11-start|
2. GUI Resources		|gui-resources|
3. Shell Commands		|gui-pty|
4. Various			|gui-x11-various|
5. GTK version			|gui-gtk|
6. GNOME version		|gui-gnome|
7. KDE version                  |gui-kde|
8. Compiling			|gui-x11-compiling|
9. X11 selection mechanism	|x11-selection|

Other relevant documentation:
|gui.txt|	For generic items of the GUI.

{Vi does not have any of these commands}

==============================================================================
1. Starting the X11 GUI					*gui-x11-start* *E665*

Then you can run the GUI version of Vim in either of these ways:
    gvim [options] [files...]
    vim -g [options] [files...]

So if you call the executable "gvim", or make "gvim" a link to the executable,
then the GUI version will automatically be used.  Additional characters may be
added after "gvim", for example "gvim-5".

You may also start up the GUI from within the terminal version by using one of
these commands:
	:gui [++opt] [+cmd] [-f|-b] [files...]			*:gu* *:gui*
	:gvim [++opt] [+cmd] [-f|-b] [files...]			*:gv* *:gvim*
The "-f" option runs Vim in the foreground.
The "-b" option runs Vim in the background (this is the default).
Also see |++opt| and |+cmd|.

							*gui-fork*
When the GUI is started, it does a fork() and exits the current process.
When gvim was started from a shell this makes the shell accept further
commands.  If you don't want this (e.g. when using gvim for a mail program
that waits for gvim to exit), start gvim with "gvim -f", "vim -gf" or use
":gui -f".  Don't use "vim -fg", because "-fg" specifies the foreground
color.

When using "gvim -f" and then ":gui", Vim will run in the foreground.  The
"-f" argument will be remembered.  To force running Vim in the background use
":gui -b".

"gvim --nofork" does the same as "gvim -f".

If you want the GUI to run in the foreground always, include the 'f'
flag in 'guioptions'.  |-f|.

==============================================================================
2. GUI Resources			*gui-resources* *.Xdefaults*

If using the Motif or Athena version of the GUI (not for the KDE, GTK+ or Win32
version), a number of X resources are available.  You should use Vim's class
"Vim" when setting these.  They are as follows:

    Resource name	Meaning		~

    reverseVideo	Boolean: should reverse video be used?
    background		Color of background.
    foreground		Color of normal text.
    scrollBackground	Color of trough portion of scrollbars.
    scrollForeground	Color of slider and arrow portions of scrollbars.
    menuBackground	Color of menu backgrounds.
    menuForeground	Color of menu foregrounds.
    tooltipForeground	Color of tooltip and balloon foreground.
    tooltipBackground	Color of tooltip and balloon background.

    font		Name of font used for normal text.
    boldFont		Name of font used for bold text.
    italicFont		Name of font used for italic text.
    boldItalicFont	Name of font used for bold, italic text.
    menuFont		Name of font used for the menus, used when compiled
			without the |+xfontset| feature
    menuFontSet		Name of fontset used for the menus, used when compiled
			with the |+xfontset| feature
    tooltipFont		Name of the font used for the tooltip and balloons.
			When compiled with the |+xfontset| feature this is a
			fontset name.

    geometry		Initial geometry to use for gvim's window (default
			is same size as terminal that started it).
    scrollbarWidth	Thickness of scrollbars.
    borderWidth		Thickness of border around text area.
    menuHeight		Height of the menu bar (only for Athena).

A special font for italic, bold, and italic-bold text will only be used if
the user has specified one via a resource.  No attempt is made to guess what
fonts should be used for these based on the normal text font.

Note that the colors can also be set with the ":highlight" command, using the
"Normal", "Menu", "Tooltip", and "Scrollbar" groups.  Example: >
	:highlight Menu guibg=lightblue
	:highlight Tooltip guibg=yellow
	:highlight Scrollbar guibg=lightblue guifg=blue
	:highlight Normal guibg=grey90
<
							*font-sizes*
Note: All fonts (except for the menu and tooltip) must be of the same size!!!
If you don't do this, text will disappear or mess up the display.  Vim does
not check the font sizes.  It's the size in screen pixels that must be the
same.  Note that some fonts that have the same point size don't have the same
pixel size!  Additionally, the positioning of the fonts must be the same
(ascent and descent).  You can check this with "xlsfonts -l {fontname}".

If any of these things are also set with Vim commands, eg with
":set guifont=Screen15", then this will override the X resources (currently
'guifont' is the only option that is supported).

Here is an example of what you might put in your ~/.Xdefaults file: >

	Vim*useSchemes:			all
	Vim*sgiMode:			true
	Vim*useEnhancedFSB:		true
	Vim.foreground:			Black
	Vim.background:			Wheat
	Vim*fontList:			7x13

The first three of these are standard resources on Silicon Graphics machines
which make Motif applications look even better, highly recommended!

The "Vim*fontList" is to set the menu font for Motif.  Example: >
	Vim*menuBar*fontList:	     -*-courier-medium-r-*-*-10-*-*-*-*-*-*-*
With Athena: >
	Vim*menuBar*SmeBSB*font:     -*-courier-medium-r-*-*-10-*-*-*-*-*-*-*
	Vim*menuBar*MenuButton*font: -*-courier-medium-r-*-*-10-*-*-*-*-*-*-*

NOTE: A more portable, and indeed more correct, way to specify the menu font
in either Motif or Athena is through the resource: >
	Vim.menuFont:	     -*-courier-medium-r-*-*-10-*-*-*-*-*-*-*
Or, when compiled with the |+xfontset| feature: >
	Vim.menuFontSet:     -*-courier-medium-r-*-*-10-*-*-*-*-*-*-*

Don't use "Vim*geometry" in the defaults.  This will break the menus.  Use
"Vim.geometry" instead.

If you get an error message "Cannot allocate colormap entry for "gray60",
try adding this to your Vim resources (change the colors to your liking): >

	Vim*scrollBackground:		Black
	Vim*scrollForeground:		Blue

The resources can also be set with arguments to Vim:

    argument		meaning	~
							*-gui*
   -display {display}	Run vim on {display}		*-display*
   -iconic		Start vim iconified		*-iconic*
   -background {color}	Use {color} for the background	*-background*
   -bg {color}		idem				*-bg*
   -foreground {color}	Use {color} for normal text	*-foreground*
   -fg {color}		idem				*-fg*
   -ul {color}		idem				*-ul*
   -font {font}		Use {font} for normal text	*-font*
   -fn {font}		idem				*-fn*
   -boldfont {font}	Use {font} for bold text	*-boldfont*
   -italicfont {font}	Use {font} for italic text	*-italicfont*
   -menufont {font}	Use {font} for menu items	*-menufont*
   -menufontset {fontset} Use {fontset} for menu items	*-menufontset*
   -mf {font}		idem				*-mf*
   -geometry {geom}	Use {geom} for initial geometry	*-geometry*
   -geom {geom}		idem, see |-geometry-example|	*-geom*
   -borderwidth {width}	Use a border width of {width}	*-borderwidth*
   -bw {width}		idem				*-bw*
							*-scrollbarwidth*
   -scrollbarwidth {width}	Use a scrollbar width of {width}
   -sw {width}		idem				*-sw*
   -menuheight {height}	Use a menu bar height of {height} *-menuheight*
   -mh {height}		idem				*-mh*
			NOTE: On Motif the value is ignored, the menu height
			is computed to fit the menus.
   -reverse		Use reverse video		*-reverse*
   -rv			idem				*-rv*
   +reverse		Don't use reverse video		*-+reverse*
   +rv			idem				*-+rv*
   -xrm {resource}	Set the specified resource	*-xrm*

Note about reverse video: Vim checks that the result is actually a light text
on a dark background.  The reason is that some X11 versions swap the colors,
and some don't.  These two examples will both give yellow text on a blue
background:
    gvim -fg Yellow -bg Blue -reverse
    gvim -bg Yellow -fg Blue -reverse

							*-geometry-example*
An example for the geometry argument: >
	gvim -geometry 80x63+8+100
This creates a window with 80 columns and 63 lines at position 8 pixels from
the left and 100 pixels from the top of the screen.

==============================================================================
3. Shell Commands					*gui-pty*

WARNING: Executing an external command from the GUI will not always work.
"normal" commands like "ls", "grep" and "make" mostly work fine.  Commands
that require an intelligent terminal like "less" and "ispell" won't work.
Some may even hang and need to be killed from another terminal.  So be
careful!

There are two ways to do the I/O with a shell command: Pipes and a pseudo-tty.
The default is to use a pseudo-tty.  This should work best on most systems.

Unfortunately, the implementation of the pseudo-tty is different on every Unix
system.  And some systems require root permission.  To avoid running into
problems with a pseudo-tty when you least expect it, test it when not editing
a file.  Be prepared to "kill" the started command or Vim.  Commands like
":r !cat" may hang!

If using a pseudo-tty does not work for you, reset the 'guipty' option: >

	:set noguipty

Using a pipe should work on any Unix system, but there are disadvantages:
- Some shell commands will notice that a pipe is being used and behave
  differently.  E.g., ":!ls" will list the files in one column.
- The ":sh" command won't show a prompt, although it will sort of work.
- When using ":make" it's not possible to interrupt with a CTRL-C.

Typeahead while the external command is running is often lost.  This happens
both with a pipe and a pseudo-tty.  This is a known problem, but it seems it
can't be fixed (or at least, it's very difficult).

							*gui-pty-erase*
When your erase character is wrong for an external command, you should fix
this in your "~/.cshrc" file, or whatever file your shell uses for
initializations.  For example, when you want to use backspace to delete
characters, but hitting backspaces produces "^H" instead, try adding this to
your "~/.cshrc": >
	stty erase ^H
The ^H is a real CTRL-H, type it as CTRL-V CTRL-H.

==============================================================================
4. Various						*gui-x11-various*

							*gui-x11-printing*
The "File/Print" menu simply sends the current buffer to "lpr".  No options or
whatever.  If you want something else, you can define your own print command.
For example: >

  :10amenu File.Print :w !lpr -Php3
  :10vmenu File.Print :w !lpr -Php3
<
							*X11-icon*
Vim uses a black&white icon by default when compiled with Motif or Athena.  A
colored Vim icon is included as $VIMRUNTIME/vim32x32.xpm.  For GTK+, this is
the builtin icon used.  Unfortunately, how you should install it depends on
your window manager.  When you use this, remove the 'i' flag from
'guioptions', to remove the black&white icon: >
  :set guioptions-=i

If you use one of the fvwm* family of window managers simply add this line to
your .fvwm2rc configuration file: >

  Style "vim"		Icon vim32x32.xpm

Make sure the icon file's location is consistent with the window manager's
ImagePath statement.  Either modify the ImagePath from within your .fvwm2rc or
drop the icon into one the pre-defined directories: >

  ImagePath /usr/X11R6/include/X11/pixmaps:/usr/X11R6/include/X11/bitmaps

Note: older versions of fvwm use "IconPath" instead of "ImagePath".

For CDE "dtwm" (a derivative of Motif) add this line in the .Xdefaults: >
   Dtwm*Vim*iconImage: /usr/local/share/vim/vim32x32.xpm

For "mwm" (Motif window manager) the line would be: >
   Mwm*Vim*iconImage: /usr/local/share/vim/vim32x32.xpm

Mouse Pointers Available in X11				*X11_mouse_shapes*

By using the |'mouseshape'| option, the mouse pointer can be automatically
changed whenever Vim enters one of its various modes (e.g., Insert or
Command).  Currently, the available pointers are:

	arrow			an arrow pointing northwest
	beam			a I-like vertical bar
	size			an arrow pointing up and down
	busy			a wristwatch
	blank			an invisible pointer
	crosshair		a thin "+" sign
	hand1			a dark hand pointing northeast
	hand2			a light hand pointing northwest
	pencil			a pencil pointing southeast
	question		question_arrow
	right_arrow		an arrow pointing northeast
	up_arrow		an arrow pointing upwards

Additionally, any of the mouse pointers that are built into X11 may be
used by specifying an integer from the X11/cursorfont.h include file.

If a name is used that exists on other systems, but not in X11, the default
"arrow" pointer is used.

==============================================================================
5. GTK version						*gui-gtk* *GTK+* *GTK*

The GTK version of the GUI works a little bit different.

GTK does _not_ use the traditional X resource settings.  Thus items in your
~/.Xdefaults or app-defaults files are not used.
Many of the traditional X command line arguments are not supported.  (e.g.,
stuff like -bg, -fg, etc).  The ones that are supported are:

    command line argument   resource name	meaning ~
    -fn  or  -font	    .font		font name for the text
    -geom  or  -geometry    .geometry		size of the gvim window
    -rv  or  -reverse	    *reverseVideo	white text on black background
    -display					display to be used
    -fg -foreground {color}			foreground color
    -bg -background {color}			background color

To set the font, see |'guifont'|.  For GTK, there's also a menu option that
does this.

Additionally, there are these command line arguments, which are handled by GTK
internally.  Look in the GTK documentation for how they are used:
	--sync
	--gdk-debug
	--gdk-no-debug
	--no-xshm	(not in GTK+ 2)
	--xim-preedit	(not in GTK+ 2)
	--xim-status	(not in GTK+ 2)
	--gtk-debug
	--gtk-no-debug
	--g-fatal-warnings
	--gtk-module
	--display	(GTK+ counterpart of -display; works the same way.)
	--screen	(The screen number; for GTK+ 2.2 multihead support.)

These arguments are ignored when the |+netbeans_intg| feature is used:
	-xrm
	-mf

As for colors, Vim's color settings (for syntax highlighting) is still
done the traditional Vim way.  See |:highlight| for more help.

If you want to set the colors of remaining gui components (e.g., the
menubar, scrollbar, whatever), those are GTK specific settings and you
need to set those up in some sort of gtkrc file.  You'll have to refer
to the GTK documentation, however little there is, on how to do this.
See http://developer.gnome.org/doc/API/2.0/gtk/gtk-Resource-Files.html
for more information.

						*gtk-tooltip-colors*
Example, which sets the tooltip colors to black on light-yellow: >

	style "tooltips"
	{
		bg[NORMAL] = "#ffffcc"
		fg[NORMAL] = "#000000"
	}

	widget "gtk-tooltips*"		style "tooltips"

Write this in the file ~/.gtkrc and it will be used by GTK+.  For GTK+ 2
you might have to use the file ~/.gtkrc-2.0 instead, depending on your
distribution.

Using Vim as a GTK+ plugin				*gui-gtk-socketid*

When the GTK+ version of Vim starts up normally, it creates its own top level
window (technically, a 'GtkWindow').  GTK+ provides an embedding facility with
its GtkSocket and GtkPlug widgets.  If one GTK+ application creates a
GtkSocket widget in one of its windows, an entirely different GTK+ application
may embed itself into the first application by creating a top-level GtkPlug
widget using the socket's ID.

If you pass Vim the command-line option '--socketid' with a decimal or
hexadecimal value, Vim will create a GtkPlug widget using that value instead
of the normal GtkWindow.  This enables Vim to act as a GTK+ plugin.

This really is a programmer's interface, and is of no use without a supporting
application to spawn the Vim correctly.  For more details on GTK+ sockets, see
http://www.gtk.org/api/

Note that this feature requires the latest GTK version.  GTK 1.2.10 still has
a small problem.  The socket feature has not yet been tested with GTK+ 2 --
feel free to volunteer.

==============================================================================
6. GNOME version				*gui-gnome* *Gnome* *GNOME*

The GNOME GUI works just like the GTK+ version.  See |GTK+| above for how it
works.  It looks a bit different though, and implements one important feature
that's not available in the plain GTK+ GUI:  Interaction with the session
manager. |gui-gnome-session|

These are the different looks:
- Uses GNOME dialogs (GNOME 1 only).  The GNOME 2 GUI uses the same nice
  dialogs as the GTK+ 2 version.
- Uses the GNOME dock, so that the toolbar and menubar can be moved to
  different locations other than the top (e.g., the toolbar can be placed on
  the left, right, top, or bottom).  The placement of the menubar and
  toolbar is only saved in the GNOME 2 version.
- That means the menubar and toolbar handles are back!  Yeah!  And the
  resizing grid still works too.

GNOME is automatically compiled with if it was found by configure.
(FIXME: Is this still true?  Use --enable-gnome-check to force it to.)

GNOME session support			*gui-gnome-session* *gnome-session*

On logout, Vim shows the well-known exit confirmation dialog if any buffers
are modified.  Clicking [Cancel] will stop the logout process.  Otherwise the
current session is stored to disk by using the |:mksession| command, and
restored the next time you log in.

The GNOME session support should also work with the KDE session manager.
If you are experiencing any problems please report them as bugs.

Note: The automatic session save works entirely transparent, in order to
avoid conflicts with your own session files, scripts and autocommands.  That
means in detail:
- The session file is stored to a separate directory (usually $HOME/.gnome2).
- 'sessionoptions' is ignored, and a hardcoded set of appropriate flags is
  used instead: >
	blank,curdir,folds,globals,help,options,winsize
- The internal variable |v:this_session| is not changed when storing the
  session.  Also, it is restored to its old value when logging in again.

The position and size of the GUI window is not saved by Vim since doing so
is the window manager's job.  But if compiled with GTK+ 2 support, Vim helps
the WM to identify the window by restoring the window role (using the |--role|
command line argument).

==============================================================================
7. KDE version					*gui-kde* *kde* *KDE* *KVim*

The KDE version of Vim works with KDE 2.x and KDE 3.x.
KVim (name code for gui-kde) does not use traditional X settings for its
configuration.
Most important difference is the font handling, KVim uses QFont to display the
text. To set your font use the following syntax :
>
  :set guifont=Fixed\ [Misc]/10/-1/5/50/0/0/0/1/0
<
the '10' value is the font size, other settings concerns more specific Qt
options which you should not need to care with.
The suggested way to choose your font is through the font selection dialog
available with the command :
  :set guifont=*

Note: X Font names are not supported any more, so if you use GVim too, you'll
have to set something like this in your ~/.gvimrc : >

  if has("gui_kde")
	:set guifont=Fixed\ [Misc]/10/-1/5/50/0/0/0/1/0
  else if has("gui_gtk")
	:set guifont=-misc-fixed-medium-r-normal-*-*-100-*-*-c-*-iso10646-1
  endif
<
							*antialias*
KVim uses antialias for its font, so that the text looks better, to disable
this you have to refer to Qt's documentation (export QT_XFT=0 for QT 2.x).

KDE provides some other features, like being able to move the menubar and the
toolbar wherever you want around the text area.

							*kde-toolbar*
KVim can be used with a KDE-look toolbar instead of Vim's default toolbar. To
enable this feature you have to run the configure script with the
--enable-kde-toolbar switch. It may be moved to a runtime option in the
future.

							*DCOP*
Since Vim 6.0, the new ClientServer feature has been added, it works fine in
KVim too. KVim also provides its own communication scheme based on DCOP. This
is mainly used by the |vimpart| but can freely be used by other applications
or manually through KDE's DCOP tools. The DCOP servername is synchronized with
the X11 servername so that it's easier to identify the same KVim through the
two communication systems.

							*vimpart* *vim-kpart*
KVim developers are also working on a component to allow embedding of Vim into
KDE's applications. As of this writing, the component is working and can be
used in different KDE applications. New KDE applications should support it
soon. To get more information about this component, refer to
http://freehackers.org/kvim or to the KDE project.

==============================================================================
8. Compiling						*gui-x11-compiling*

If using X11, Vim's Makefile will by default first try to find the necessary
GTK+ files on your system.  If the GTK+ files cannot be found, then the Motif
files will be searched for.  Finally, if this fails, the Athena files will be
searched for.  If all three fail, the GUI will be disabled.

For GTK+, Vim's configuration process requires that GTK+ be properly
installed.  That is, the shell script 'gtk-config' must be in your PATH, and
you can already successful compile, build, and execute a GTK+ program.  The
reason for this is because the compiler flags (CFLAGS) and link flags
(LDFLAGS) are obtained through the 'gtk-config' shell script.

If you want to build with GTK+ 2 support pass the --enable-gtk2-check argument
to ./configure.  Optionally, support for GNOME 2 will be compiled if the
--enable-gnome-check option is also given.  Note that the support for GTK+ 2
is still experimental.  However, many people have reported that it works just
fine for them.

Otherwise, if you are using Motif or Athena, when you have the Motif or Athena
files in a directory where configure doesn't look, edit the Makefile to enter
the names of the directories.  Search for "GUI_INC_LOC" for an example to set
the Motif directories, "CONF_OPT_X" for Athena.

							*gui-x11-gtk*
At the time of this writing, you may use either GTK+ version 1.0.6 or 1.2.  It
is suggested that you use v1.2 since not all of Vim's GUI features are present
if using v1.0.6.  For instance, there are no tearoff menus present in v1.0.6.
Using a version from GTK+'s CVS tree may or may not work, and is therefore not
supported and not recommended.

For the experimental GTK+ 2 GUI, using the latest release of the GTK+ 2.0 or
GTK+ 2.2 series is recommended.  CVS HEAD seems to work fine most of time as
well.

Lastly, although GTK+ has supposedly been ported to the Win32 platform, this
has not been tested with Vim and is also unsupported.  Also, it's unlikely to
even compile since GTK+ GUI uses parts of the generic X11 code.  This might
change in distant future; particularly because getting rid of the X11 centric
code parts is also required for GTK+ framebuffer support.

							*gui-x11-motif*
For Motif, you need at least Motif version 1.2 and/or X11R5.  Motif 2.0 and
X11R6 are OK.  Motif 1.1 and X11R4 might work, no guarantee (there may be a
few problems, but you might make it compile and run with a bit of work, please
send me the patches if you do).  The newest releases of LessTif have been
reported to work fine too.

							*gui-x11-athena*
The Athena version uses the Xaw widget set by default.  If you have the 3D
version, you might want to link with Xaw3d instead.  This will make the
menus look a bit better.  Edit the Makefile and look for "XAW_LIB".  The
scrollbars will remain the same, because Vim has its own, which are already
3D (in fact, they look more like Motif).

							*gui-x11-kde*
For Vim-KDE, you need at least Qt(>=2.x) and the corresponding kdelibs.
To compile, you must use the --with-qt-dir configure flag because QTDIR is not
automatically detected yet. Giving KDE's directories to the configure script
may also help in some cases.

							*gui-x11-neXtaw*
The neXtaw version is mostly like Athena, but uses different widgets.

							*gui-x11-misc*
In general, do not try to mix files from different GTK+, Motif, Athena and X11
versions.  This will cause problems.  For example, using header files for
X11R5 with a library for X11R6 probably doesn't work (although the linking
won't give an error message, Vim will crash later).

==============================================================================
9. X11 selection mechanism				*x11-selection*

If using X11, in either the GUI or an xterm with an X11-aware Vim, then Vim
provides varied access to the X11 selection and clipboard.  These are accessed
by using the two selection registers "* and "+.

X11 provides two basic types of global store, selections and cut-buffers,
which differ in one important aspect: selections are "owned" by an
application, and disappear when that application (e.g., Vim) exits, thus
losing the data, whereas cut-buffers, are stored within the X-server itself
and remain until written over or the X-server exits (e.g., upon logging out).

The contents of selections are held by the originating application (e.g., upon
a copy), and only passed on to another application when that other application
asks for them (e.g., upon a paste).

The contents of cut-buffers are immediately written to, and are then
accessible directly from the X-server, without contacting the originating
application.

							*quoteplus* *quote+*
There are three documented X selections: PRIMARY (which is expected to
represent the current visual selection - as in Vim's Visual mode), SECONDARY
(which is ill-defined) and CLIPBOARD (which is expected to be used for
cut, copy and paste operations).

Of these three, Vim uses PRIMARY when reading and writing the "* register
(hence when the X11 selections are available, Vim sets a default value for
|'clipboard'| of "autoselect"), and CLIPBOARD when reading and writing the "+
register.  Vim does not access the SECONDARY selection.

Examples: (assuming the default option values)
- Select an URL in Visual mode in Vim.  Go to a text field in Netscape and
  click the middle mouse button.  The selected text will be inserted
  (hopefully!).
- Select some text in Netscape by dragging with the mouse.  Go to Vim and
  press the middle mouse button: The selected text is inserted.
- Select some text in Vim and do "+y.  Go to Netscape, select some text in a
  textfield by dragging with the mouse.  Now use the right mouse button and
  select "Paste" from the popup menu.  The selected text is overwritten by the
  text from Vim.
Note that the text in the "+ register remains available when making a Visual
selection, which makes other text available in the "* register.  That allows
overwriting selected text.
							*x11-cut-buffer*
There are, by default, 8 cut-buffers: CUT_BUFFER0 to CUT_BUFFER7.  Vim only
uses CUT_BUFFER0, which is the one that xterm uses by default.

Whenever Vim is about to become unavailable (either via exiting or becoming
suspended), and thus unable to respond to another application's selection
request, it writes the contents of any owned selection to CUT_BUFFER0.  If the
"+ CLIPBOARD selection is owned by Vim, then this is written in preference,
otherwise if the "* PRIMARY selection is owned by Vim, then that is written.

Similarly, when Vim tries to paste from "* or "+ (either explicitly, or, in
the case of the "* register, when the middle mouse button is clicked), if the
requested X selection is empty or unavailable, Vim reverts to reading the
current value of the CUT_BUFFER0.

Note that when text is copied to CUT_BUFFER0 in this way, the type of
selection (character, line or block) is always lost, even if it is a Vim which
later pastes it.

Xterm, by default, always writes visible selections to both PRIMARY and
CUT_BUFFER0.  When it pastes, it uses PRIMARY if this is available, or else
falls back upon CUT_BUFFER0.  For this reason, when cutting and pasting
between Vim and an xterm, you should use the "* register.  Xterm doesn't use
CLIPBOARD, thus the "+ doesn't work with xterm.

Most newer applications will provide their current selection via PRIMARY ("*)
and use CLIPBOARD ("+) for cut/copy/paste operations.  You thus have access to
both by choosing to use either of the "* or "+ registers.


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