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+\input texinfo                  @c -*-texinfo-*-
+@c documentation for Ediff
+@c Written by Michael Kifer
+
+@comment %**start of header (This is for running Texinfo on a region.)
+
+@comment Using ediff.info instead of ediff in setfilename breaks DOS.
+@setfilename ../info/ediff.info
+@comment @setfilename ediff.info
+
+@settitle Ediff User's Manual
+@synindex vr cp
+@synindex fn cp
+@synindex pg cp
+@iftex
+@finalout
+@end iftex
+@c      @smallbook
+@comment %**end of header (This is for running Texinfo on a region.)
+
+@ifinfo
+This file documents Ediff, a comprehensive visual interface to Unix diff
+and patch utilities.
+
+Permission is granted to make and distribute verbatim copies of this
+manual provided the copyright notice and this permission notice are
+preserved on all copies.
+
+@ignore
+Permission is granted to process this file through TeX and print the
+results, provided the printed document carries copying permission notice
+identical to this one except for the removal of this paragraph (this
+paragraph not being relevant to the printed manual).
+
+@end ignore
+@end ifinfo
+
+@iftex
+@titlepage
+@title Ediff User's Manual
+@sp 4
+@subtitle Ediff version 2.61
+@sp 1
+@subtitle June 1996
+@sp 5
+@author Michael Kifer
+@page
+
+@vskip 0pt plus 1filll
+@noindent
+Copyright @copyright{} 1995, 1996 Free Software Foundation, Inc.
+
+Permission is granted to make and distribute verbatim copies of
+this manual provided the copyright notice and this permission notice
+are preserved on all copies.
+@end titlepage
+@page
+@end iftex
+
+@node Top, Introduction, (dir), (dir)
+
+@menu
+* Introduction::                About Ediff.
+* Major Entry Points::          How to use Ediff.
+* Commands::                    Ediff commands.
+* Registry of Ediff Sessions::  Keeping track of multiple Ediff sessions.
+* Session Groups::              Comparing and merging directories.
+* Remote and Compressed Files::  You may want to know about this.
+* Customization::               How to make Ediff work the way YOU want.
+* Credits::                     Thanks to those who helped.
+* Index::                       
+@end menu
+
+@node Introduction, Major Entry Points, Top, Top
+@chapter Introduction
+
+@cindex Comparing files and buffers
+@cindex Merging files and buffers
+@cindex Patching files and buffers
+@cindex Finding differences
+
+Ediff provides a convenient way for simultaneous browsing through
+the differences between a pair (or a triple) of files or buffers.  The
+files being compared, file-A, file-B, and file-C (if applicable) are
+shown in separate windows (side by side, one above the another, or in
+separate frames), and the differences are highlighted as you step
+through them.  You can also copy difference regions from one buffer to
+another (and recover old differences if you change your mind).
+
+Another powerful feature is the ability to merge a pair of files into a
+third buffer. Merging with an ancestor file is also supported.
+Furthermore, Ediff is equipped with directory-level capabilities that
+allow the user to conveniently launch browsing or merging sessions on
+groups of files in two (or three) different directories.
+
+In addition, Ediff can apply a patch to a file and then let you step though
+both files, the patched and the original one, simultaneously,
+difference-by-difference.  You can even apply a patch right out of a mail
+buffer, i.e., patches received by mail don't even have to be saved.  Since
+Ediff lets you copy differences between buffers, you can, in effect, apply
+patches selectively (i.e., you can copy a difference region from
+@file{file_orig} to @file{file}, thereby undoing any particular patch that
+you don't like).
+
+Ediff even understands multi-file patches and can apply them interactively!
+(Ediff can recognize multi-file patches only if they are in the context or
+GNU unified format. All other patches are treated as 1-file patches. Ediff
+is [hopefully] using the same algorithm as patch to determine which
+files need to be patched.)
+
+Ediff is aware of version control, which lets you compare
+files with their older versions. Ediff also works with remote and
+compressed files, automatically ftp'ing them over and uncompressing them.
+@xref{Remote and Compressed Files}, for details.
+
+This package builds upon ideas borrowed from Emerge and
+several Ediff's functions are adaptations from Emerge.
+Although Ediff subsumes Emerge,
+much of the functionality of Ediff is influenced by Emerge.
+The architecture and the interface are, of course, drastically different.
+
+@node Major Entry Points, Commands, Introduction, Top
+@chapter Major Entry Points
+
+Ediff can be invoked interactively using the following functions, which can
+be run either from the minibuffer or from the menu bar. In the menu bar,
+all Ediff's entry points belong to three submenus of the Tools menu:
+Compare, Merge, and Apply Patch.
+
+@table @code
+@item ediff-files
+@itemx ediff
+@findex ediff-files
+@findex ediff
+Compare two files.
+
+@item ediff-buffers
+@findex ediff-buffers
+Compare two buffers.
+
+@item ediff-files3
+@itemx ediff3
+@findex ediff-files3
+@findex ediff3
+Compare three files.
+
+@item ediff-buffers3
+@findex ediff-buffers3
+Compare three buffers.
+
+@item edirs
+@itemx ediff-directories
+@findex edirs
+@findex ediff-directories
+ Compare files common to two directories.
+@item edirs3
+@itemx ediff-directories3
+@findex edirs3
+@findex ediff-directories3
+ Compare files common to three directories.
+@item edir-revisions
+@itemx ediff-directory-revisions
+@findex ediff-directory-revisions
+@findex edir-revisions
+ Compare versions of files in a given directory. Ediff selects only the
+files that are under version control.
+@item edir-merge-revisions
+@itemx ediff-merge-directory-revisions
+@findex edir-merge-revisions
+@findex ediff-merge-directory-revisions
+ Merge versions of files in a given directory. Ediff selects only the
+files that are under version control.
+@item edir-merge-revisions-with-ancestor
+@itemx ediff-merge-directory-revisions-with-ancestor
+@findex edir-merge-revisions-with-ancestor
+@findex ediff-merge-directory-revisions-with-ancestor
+ Merge versions of files in a given directory using other versions as
+ancestors. Ediff selects only the files that are under version control.
+
+@item ediff-windows-wordwise
+@findex ediff-windows-wordwise
+Compare windows word-by-word.
+
+@item ediff-windows-linewise
+@findex ediff-windows-linewise
+Compare windows line-by-line.
+
+@item ediff-regions-wordwise
+@findex ediff-regions-wordwise
+Compare regions word-by-word.
+
+@item ediff-regions-linewise
+@findex ediff-regions-linewise
+Compare regions line-by-line.
+
+@item ediff-revision
+@findex ediff-revision
+ Compare versions of the current buffer, if the buffer is visiting
+ a file under version control. 
+
+@item ediff-patch-file
+@itemx epatch
+@findex ediff-patch-file
+@findex epatch
+ Patch a file, then compare.
+@item ediff-patch-buffer
+@itemx epatch-buffer
+@findex ediff-patch-buffer
+Patch a buffer, then compare.
+
+@item ediff-merge-files
+@itemx ediff-merge
+@findex ediff-merge-files
+@findex ediff-merge
+Merge two files.
+
+@item ediff-merge-files-with-ancestor
+@itemx ediff-merge-with-ancestor
+@findex ediff-merge-files-with-ancestor
+@findex ediff-merge-with-ancestor
+Like @code{ediff-merge}, but with a third ancestor file.
+
+@item ediff-merge-buffers
+@findex ediff-merge-buffers
+Merge two buffers.
+
+@item ediff-merge-buffers-with-ancestor
+@findex ediff-merge-buffers-with-ancestor
+Same but with ancestor.
+
+
+@item edirs-merge
+@itemx ediff-merge-directories
+@findex edirs-merge
+@findex ediff-merge-directories
+ Merge files common to two directories.
+@item edirs-merge-with-ancestor
+@itemx ediff-merge-directories-with-ancestor
+@findex edirs-merge-with-ancestor
+@findex ediff-merge-directories-with-ancestor
+ Same but using files in a third directory as ancestors.
+
+@item ediff-merge-revisions
+@findex ediff-merge-revisions
+Merge two versions of the file visited by the current buffer.
+
+@item ediff-merge-revisions-with-ancestor
+@findex ediff-merge-revisions-with-ancestor
+Same but with ancestor.
+@end table
+
+@noindent
+If you want Ediff to be loaded from the very beginning of your Emacs
+session, you should put this line in your @file{~/.emacs} file:
+
+@example
+(require 'ediff)
+@end example
+
+@noindent
+Otherwise, Ediff will be loaded automatically when you use one of the
+above functions, either directly or through the menus.
+
+When the above functions are invoked, they prompt the user for the
+information they need---typically the files or buffers to compare or
+patch. Ediff tries to be smart about these prompts. For instance, in
+comparing/merging files, it will offer the visible buffers as defaults.  In
+prompting for files, if the user enters a directory, the previously input
+file name will be appended to that directory. In addition, if the variable
+@code{ediff-use-last-dir} is not @code{nil}, Ediff will offer 
+previously entered directories as defaults (which will be maintained
+separately for each type of file, A, B, or C).
+@vindex @code{ediff-use-last-dir}
+
+All the above functions use the POSIX @code{diff} program to find
+differences between two files.  They process the @code{diff} output and
+display it in a convenient form.  At present, Ediff understands only the
+plain output from diff.  Options such as @samp{-c} are not supported,
+nor is the format produced by incompatible file comparison programs such
+as the VMS version of @code{diff}.
+
+The functions @code{ediff-files}, @code{ediff-buffers},
+@code{ediff-files3}, @code{ediff-buffers3} first display the coarse,
+line-based difference regions, as reported by the @file{diff} program.
+Since diff may report fairly large chunks of text as being different,
+even though the difference may be localized to just a few words or even
+to the white space or line breaks, Ediff further @emph{refines} the
+regions to indicate which exact words differ.  If the only difference is
+in the white space and line breaks, Ediff says so.
+
+On a color display, fine differences are highlighted with color; on a
+monochrome display, they are underlined.  @xref{Highlighting Difference
+Regions}, for information on how to customize this.
+
+The functions @code{ediff-windows-wordwise},
+@code{ediff-windows-linewise}, @code{ediff-regions-wordwise} and
+@code{ediff-regions-linewise} do comparison on parts of existing Emacs
+buffers.  Since @code{ediff-windows-wordwise} and
+@code{ediff-regions-wordwise} are intended for relatively small segments
+of buffers, comparison is done on the basis of words rather than lines.
+No refinement is necessary in this case.  These commands are recommended
+only for relatively small regions (perhaps, up to 100 lines), because
+these functions have a relatively slow startup.
+
+To compare large regions, use @code{ediff-regions-linewise}.  This
+command displays differences much like @code{ediff-files} and
+@code{ediff-buffers}.
+
+The functions @code{ediff-patch-file} and @code{ediff-patch-buffer} apply a
+patch to a file or a buffer and then run Ediff on these buffers, displaying
+the difference regions. 
+
+The entry points @code{ediff-directories}, @code{ediff-merge-directories},
+etc., provide a convenient interface for comparing and merging files in
+different directories. The user is presented with Dired-like interface from
+which one can run a group of related Ediff sessions.
+
+For files under version control, @code{ediff-revisions} lets you compare
+the file visited by the current buffer to one of its checked-in versions.
+You can also compare two checked-in versions of the visited file.
+Moreover, the functions @code{ediff-directory-revisions},
+@code{ediff-merge-directory-revisions}, etc., let you run a group of
+related Ediff sessions by taking a directory and comparing (or merging)
+versions of files in that directory.
+
+@node Commands, Registry of Ediff Sessions, Major Entry Points, Top
+@chapter Commands
+
+All Ediff commands are displayed in a quick
+help window, unless you type @kbd{?} to shrink the window to just one line.
+You can redisplay the help window by typing @kbd{?} again.
+In this section
+we comment only on the features that cannot be readily deduced from the
+quick help window.
+You can always type @kbd{E} in the control window to display this manual.
+
+Many Ediff commands take numeric prefix arguments.  For instance, if you
+type a number, say 3, and then @kbd{j} (@code{ediff-jump-to-difference}), Ediff
+moves to the third difference region.   Typing 3 and then @kbd{a}
+(@code{ediff-diff-to-diff}) copies the 3d difference region from buffer
+A to buffer B.  Typing @kbd{b} does copying in the opposite
+direction.  (In 3-way comparison mode, the commands for copying are
+@kbd{ab}, @kbd{ba}, @kbd{ca}, etc.)
+Likewise, 4 followed by @kbd{ra}
+restores the 4th difference region in buffer A (if it was previously
+saved as a result of copying from, say, buffer B to A).
+
+Some commands take negative prefix arguments as well.
+For instance, typing @kbd{-} and then @kbd{j} will take Ediff to the last
+difference. Typing @kbd{-2} then @kbd{j} takes Ediff to to the penultimate
+difference region, etc.
+
+Without the prefix argument, all commands operate on the current
+selected difference region.  You can select any difference region
+as the current one using other Ediff commands.
+
+For some commands, the value of the prefix argument is immaterial. However,
+if supplied, the prefix argument modifies the command.  For instance,
+normally the commands @kbd{ga}/@kbd{gb}/@kbd{gc}
+(@code{ediff-jump-to-difference-at-point}) causes Ediff to jump to the
+difference region that is closest to the point in a specified buffer (the
+buffer, A, B, or C, is specified by the last character of the command,
+i.e., for @code{gb}, the specified buffer is B).
+However, with a prefix argument, Ediff would position all these
+buffers around the area indicated by the current point in the specified
+buffer: if the point is inside a difference region, then the buffers will
+be positioned at this difference region. If the point is not in any
+difference region, then it is in an area where all buffers agree with each
+other. In this case, all buffers will be positioned so that they would
+display this area.
+
+The total number of differences and the current difference number are
+always displayed in the mode line of the control window. 
+
+If, after making changes to buffers A, B, or C, you decide to save them, it
+is best to use @code{ediff-save-buffer}, which is bound to @kbd{wa},
+@kbd{wb}, and @kbd{wc} (@kbd{wa} will save buffer A, @kbd{wb} saves buffer
+B, etc.).
+
+Typing @kbd{wd} saves the output from the @code{diff} utility to a file, so
+you can later refer to it. With prefix argument, this command saves the
+plain output from @file{diff} (see @code{ediff-diff-program} and
+@code{ediff-diff-options}). Without the argument, it saves customized
+@file{diff} output (see @code{ediff-custom-diff-program} and
+@code{ediff-custom-diff-options}), if it is available.
+
+Instead of saving it, @file{diff} output can be @emph{displayed} using the
+command @kbd{D}. Without the prefix argument, it displays the customized
+@file{diff} output of the session.  With the prefix argument, it displays
+the plain @file{diff} output If either of the @file{diff} outputs is
+unavailable (because it wasn't generated or the user killed the respective
+buffer), then Ediff will try to display the other @file{diff} output.  If
+none is available, a warning is issued.
+
+The command @kbd{z} suspends the current ediff session. It hides the
+control buffer and the variants. The easiest way to resume a suspended
+Ediff session is through the registry of active sessions.
+@xref{Registry of Ediff Sessions}, for details.
+
+The command @kbd{q} quits the current Ediff session. With a prefix
+argument, it will ask the user whether to delete the variant
+buffers. 
+
+The command @kbd{s} is used only for merging.  It shrinks window C (the
+merge window) to its minimal size, thereby exposing as much of buffers A
+and B as possible.  This command is intended only for temporary viewing;
+therefore, Ediff restores window C to its original size whenever it
+makes any other change in the window configuration.  Typing @kbd{s}
+again also restores the original size of window C.  However, recentering and
+jumping to a difference does not affect window C's size.
+
+With a positive prefix argument, the command @kbd{s} makes the merge
+window, window C, slightly taller. With @kbd{-} or a negative prefix
+argument, @kbd{s} makes window C slightly shorter.
+
+Another command used only for merging is @kbd{+}.  Its effect is to
+combine the current difference regions of buffers A and B and put the
+combination into the merge buffer. @xref{Merging and diff3}, specifically,
+the variables @code{ediff-combine-diffs} and
+@code{ediff-combination-pattern}.
+
+In merge mode, Ediff uses a default variant (one of the two files being
+merged) when it cannot decide which of the difference regions (that of
+buffer A or buffer B) should be copied into the merge buffer.  You might
+decide to use the other variant instead.  To facilitate this, Ediff has
+a command, bound to @kbd{&}, which selects another default variant for
+the current difference and subsequent differences.  You can specify as
+the new default any of @samp{default-A}, @samp{default-B}, or
+@samp{combined}.  @xref{Merging and diff3}, for details.
+
+Such repeated merging affects only difference regions that have
+default-A/B status, and only if they were not changed with respect to
+their originals.
+
+Some commands are not bound to any key:
+
+@table @code
+@item eregistry
+@itemx ediff-show-registry
+@findex eregistry
+@findex ediff-show-registry
+This command brings up the registry of active Ediff sessions.  Ediff
+registry is a useful device that can be used for resuming Ediff sessions
+when the user switched to some other work before finishing a comparison or
+merging job.  It is also useful for switching between multiple active Ediff
+sessions that are run at the same time. The function @code{eregistry} is an
+alias for @code{ediff-show-registry}.
+@item ediff-toggle-multiframe
+@findex ediff-toggle-multiframe
+Changes the display from the multi-frame mode (where the quick help window
+is in a separate frame) to the single-frame mode (where all Ediff buffers
+share the same frame), and vice versa.
+@item ediff-revert-buffers-then-recompute-diffs
+@findex ediff-revert-buffers-then-recompute-diffs
+This command reverts the buffers you are comparing and recomputes their
+differences.  It is useful when, after making changes, you decided to
+make a fresh start, or if at some point you changed the files being
+compared but want to discard any changes to comparison buffers that were
+done since then.
+
+This command normally asks for confirmation before reverting files.
+With a prefix argument, it reverts files without asking.
+
+
+@item ediff-profile
+@findex ediff-profile
+Ediff has an admittedly primitive (but useful) facility for profiling
+Ediff's commands.  It is meant for Ediff maintenance---specifically, for
+making it run faster.  The function @code{ediff-profile} toggles
+profiling of ediff commands.
+@end table
+
+@node Registry of Ediff Sessions, Session Groups, Commands, Top
+@chapter Registry of Ediff Sessions
+
+Ediff maintains a registry of all its invocations that are
+still @emph{active}. This feature is very convenient for switching among
+active Ediff sessions or for quickly restarting a suspended Ediff session.
+
+The focal point of this activity is a buffer
+called @emph{*Ediff Registry*}. You can display this buffer by typing
+@kbd{R} in any Ediff Control Buffer or Session Group Buffer
+(@pxref{Session Groups}), or by typing
+@kbd{M-x eregistry} into the Minibuffer.
+The latter would be the fastest way to bring up the registry
+buffer if no control or group buffer is displayed in any of the visible
+Emacs windows.
+If you are in a habit of running multiple long Ediff sessions and often need to
+suspend, resume, or switch between them, it may be a good idea to have the
+registry buffer permanently displayed in a separate, dedicated window.
+
+The registry buffer has several convenient key bindings.
+For instance, clicking mouse button 2 or typing
+@kbd{RET} or @kbd{v} over any session record resumes that session.
+Session records in the registry buffer provide a fairly complete
+description of each session, so it is usually easy to identify the right
+session to resume.
+
+Other useful commands are bound to @kbd{SPC} (next registry record)
+and @kbd{DEL} (previous registry record). There are other commands as well,
+but you don't need to memorize them, since they are listed at the top of
+the registry buffer.
+
+@node Session Groups, Remote and Compressed Files, Registry of Ediff Sessions, Top
+@chapter Session Groups
+
+Several major entries of Ediff perform comparison and merging on
+directories.  On entering @code{ediff-directories},
+@code{ediff-directories3},
+@code{ediff-merge-directories},
+@code{ediff-merge-directories-with-ancestor},
+@code{ediff-directory-revisions},
+@code{ediff-merge-directory-revisions}, or
+@code{ediff-merge-directory-revisions-with-ancestor},
+the user is presented with a
+Dired-like buffer that lists files common to the directories involved along
+with their sizes. (The list of common files can be further filtered through
+a regular expression, which the user is prompted for.) We call this buffer
+@emph{Session Group Panel} because all Ediff sessions associated with the
+listed files will have this buffer as a common focal point.
+
+Clicking button 2 or typing @kbd{RET} or @kbd{v} over a
+record describing files invokes Ediff in the appropriate mode on these
+files. You can come back to the session group buffer associated with a
+particular invocation of Ediff by typing @kbd{M} in Ediff control buffer of
+that invocation.
+
+Many commands are available in the session group buffer; some are
+applicable only for certain types of work. The relevant commands are always
+listed at the top of each session group buffer, so there is no need to
+memorize them.
+
+In directory comparison or merging, a session group panel displays only the
+files common to all directories involved. The differences are kept in a
+separate buffer and are conveniently displayed by typing @kbd{D} to the
+corresponding session group panel. Thus, as an added benefit, Ediff can be
+used to compare the contents of up to three directories.
+
+Session records in session group panels are also marked with @kbd{+}, for
+active sessions, and with @kbd{-}, for finished sessions.  
+
+Sometimes, it is convenient to exclude certain session records from a group.
+Usually this happens when the user doesn't intend to run Ediff of certain
+files in the group, and the corresponding session records just add clutter
+to the session group buffer. To help alleviate this problem, the user can
+type @kbd{h} to mark a session as a candidate for exclusion and @kbd{x} to
+actually hide the marked sessions. There actions are reversible: with a
+prefix argument, @kbd{h} unmarks the session under the cursor, and @kbd{x}
+brings the hidden sessions into the view (@kbd{x} doesn't unmark them,
+though, so the user has to explicitly unmark the sessions of interest).
+
+Group sessions also understand the command @kbd{m}, which marks sessions
+for future operations (other than hiding) on a group of sessions. At present,
+the only such group-level operation is the creation of a multi-file patch.
+
+@cindex Multi-file patches
+A multi-file patch is a concatenated output of several runs of the Unix
+@file{diff} command (some versions of @file{diff} let you create a
+multi-file patch in just one run).  In a session group buffer created in
+response to @code{ediff-directories} or @code{ediff-directory-revisions},
+the user can type @kbd{P} to create a multi-file patch of marked sessions
+(which must be marked using the @kbd{m} command).  Ediff then will display
+a buffer containing the patch.  In an @code{ediff-directories} session, it
+is enough to just mark the requisite sessions. In
+@code{ediff-directory-revisions} revisions, the marked sessions must also
+be active, or else Ediff will refuse to produce a multi-file patch. This is
+because, in the latter-style sessions, there are many ways to create diff
+output, and it is easier to handle by running Ediff on the inactive
+sessions.
+
+
+@node Remote and Compressed Files, Customization, Session Groups, Top
+@chapter Remote and Compressed Files
+
+Ediff works with remote, compressed, and encrypted files.  Ediff
+supports @file{ange-ftp.el}, @file{jka-compr.el}, @file{uncompress.el}
+and @file{crypt++.el}, but it may work with other similar packages as
+well.  This means that you can compare files residing on another
+machine, or you can apply a patch to a file on another machine.  Even
+the patch itself can be a remote file!
+
+When patching compressed or remote files, Ediff does not rename the source
+file (unlike what the @code{patch} utility would usually do).  Instead, the
+source file retains its name and the result of applying the patch is placed
+in a temporary file that has the suffix @file{_patched} attached.
+Generally, this applies to files that are handled using black magic, such
+as special file handlers (ange-ftp and some compression and encryption
+packages all use this method).
+
+Regular files are treated by the @code{patch} utility in the usual manner,
+i.e., the original is renamed into @file{source-name.orig} and the result
+of the patch is placed into the file source-name. (Ediff @file{_orig}
+on systems like VMS, DOS, etc.)
+
+@node Customization, Credits, Remote and Compressed Files, Top
+@chapter Customization
+
+Ediff has a rather self-explanatory interface, and in most cases you
+won't need to change anything.  However, should the need arise, there are
+extensive facilities to change the default behavior.
+
+Most of the customization can be done by setting various variables in the
+@file{.emacs} file. Some customization (mostly window-related
+customization and faces) can be done by putting appropriate lines in
+@file{.Xdefaults}, @file{.xrdb}, or whatever X resource file is in use.
+
+With respect to the latter, please note that the X resource
+for Ediff customization is `Ediff', @emph{not} `emacs'.
+@xref{Window and Frame Configuration},
+@xref{Highlighting Difference Regions}, for further details. Please also
+refer to Emacs manual for the information on how to set Emacs X resources.
+
+@menu
+* Hooks::                       Customization via the hooks.
+* Quick Help::                  How to customize Ediff's quick help feature.
+* Window and Frame Configuration::  Controlling the way Ediff displays things.
+* Selective Browsing::          Advanced browsing through difference regions.
+* Highlighting Difference Regions::  Controlling highlighting.
+* Narrowing::                   Comparing regions, windows, etc.
+* Refinement of Difference Regions::  How to control the refinement process.
+* Patch and Diff Programs::     Changing the utilities that compute differences
+                                and apply patches.
+* Merging and diff3::           How to customize Ediff in its Merge Mode.
+* Support for Version Control::  Changing the version control package.
+                                 You are not likely to do that.
+* Customizing the Mode Line::   Changing the look of the mode line in Ediff.
+* Miscellaneous::               Other customization.
+* Notes on Heavy-duty Customization::  Customization for the gurus.
+@end menu
+
+@node Hooks, Quick Help, Customization, Customization
+@section Hooks
+
+The bulk of customization can be done via the following hooks:
+
+@table @code
+@item ediff-load-hook
+@vindex ediff-load-hook
+This hook can be used to change defaults after Ediff is loaded.
+
+@item ediff-keymap-setup-hook
+@vindex ediff-keymap-setup-hook
+This hook can be used to alter bindings in Ediff's keymap. These hooks are
+run right after the default bindings are set but before
+@code{ediff-load-hook}.  The regular user needs not be concerned with this
+hook---it is provided for implementors of other Emacs packages built on top
+of Ediff.
+
+@item ediff-before-setup-windows-hook
+@itemx ediff-after-setup-windows-hook
+@vindex ediff-before-setup-windows-hook
+@vindex ediff-after-setup-windows-hook
+These two hooks are called before and after Ediff sets up its window
+configuration.  Can be used to save the configuration that existed
+before Ediff starts or for whatever other purposes.
+
+@item ediff-suspend-hook
+@itemx ediff-quit-hook
+@vindex ediff-suspend-hook
+@vindex ediff-quit-hook
+These two hooks are run when you suspend or quit Ediff.  They can be
+used to set desired window configurations, delete files Ediff didn't
+want to clean up after exiting, etc.
+
+By default, @code{ediff-quit-hook} holds one hook function,
+@code{ediff-cleanup-mess}, which cleans after Ediff, as appropriate in
+most cases.  You probably won't want to change it, but you might
+want to add other hook functions.
+
+Keep in mind that hooks executing before @code{ediff-cleanup-mess} start
+in @code{ediff-control-buffer;} they should also leave
+@code{ediff-control-buffer} as the current buffer when they finish.
+Hooks that are executed after @code{ediff-cleanup-mess} should expect
+the current buffer be either buffer A or buffer B.
+@code{ediff-cleanup-mess} doesn't kill the buffers being compared or
+merged (see @code{ediff-cleanup-hook}, below).
+
+@item ediff-cleanup-hook
+@vindex ediff-cleanup-hook
+This hook is run just before @code{ediff-quit-hook}.  This is a good
+place to do various cleanups, such as deleting the variant buffers.
+Ediff provides a function, @code{ediff-janitor}, as one such possible
+hook, which you can add to @code{ediff-cleanup-hook} with
+@code{add-hooks}.
+
+@findex ediff-janitor
+This function kills buffers A, B, and, possibly, C, if these buffers aren't
+modified. In merge jobs, buffer C is never deleted.  However, the side
+effect of using this function is that you may not be able to compare the
+same buffer in two separate Ediff sessions: quitting one of them will
+delete this buffer in another session as well.
+
+@item ediff-before-setup-control-frame-hook
+@itemx ediff-after-setup-control-frame-hook
+@vindex ediff-before-setup-control-frame-hook
+@vindex ediff-after-setup-control-frame-hook
+These two hooks run before and after Ediff sets up the control frame.
+They can be used to relocate Ediff control frame when Ediff runs in a
+multiframe mode (i.e., when the control buffer is in its own dedicated
+frame).  Be aware that many variables that drive Ediff are local to
+Ediff Control Panel (@code{ediff-control-buffer}), which requires
+special care in writing these hooks.  Take a look at
+@code{ediff-default-suspend-hook} and @code{ediff-default-quit-hook} to
+see what's involved.
+
+@item ediff-startup-hook
+@vindex ediff-startup-hook
+This hook is run at the end of Ediff startup.
+
+@item ediff-select-hook
+@vindex ediff-select-hook
+This hook is run after Ediff selects the next difference region.
+
+@item ediff-unselect-hook
+@vindex ediff-unselect-hook
+This hook is run after Ediff unselects the current difference region.
+
+@item ediff-prepare-buffer-hook
+@vindex ediff-prepare-buffer-hook
+This hook is run for each Ediff buffer (A, B, C) right after the buffer
+is arranged.
+
+@item ediff-display-help-hook
+@vindex ediff-display-help-hook
+Ediff runs this hook each time after setting up the help message.  It
+can be used to alter the help message for custom packages that run on
+top of Ediff.
+
+@item ediff-mode-hook
+@vindex ediff-mode-hook
+This hook is run just after Ediff mode is set up in the control
+buffer. This is done before any Ediff window is created. You can use it to
+set local variables that alter the look of the display.
+
+@item ediff-registry-setup-hook
+@vindex ediff-registry-setup-hook
+Hooks run after setting up the registry for all active Ediff session.
+@xref{Session Groups}, for details.
+@item ediff-session-group-setup-hook
+@vindex ediff-session-group-setup-hook
+Hooks run after setting up a control panel for a group of related Ediff
+sessions. @xref{Session Groups}, for details.
+@end table
+
+@node Quick Help, Window and Frame Configuration, Hooks, Customization
+@section Quick Help
+@vindex ediff-use-long-help-message
+@vindex ediff-control-buffer
+@vindex ediff-startup-hook
+@vindex ediff-help-message
+
+Ediff provides quick help using its control panel window. Since this window
+takes a fair share of the screen real estate, you can toggle it off by
+typing @kbd{?}.  The control window will then shrink to just one line and a
+mode line, displaying a short help message.
+
+The variable @code{ediff-use-long-help-message} tells Ediff whether
+you use the short message or the long one.  By default, it
+is set to @code{nil}, meaning that the short message is used.
+Set this to @code{t}, if you want Ediff to use the long
+message by default. This property can always be changed interactively, by
+typing @kbd{?} into Ediff Control Buffer.
+
+If you want to change the appearance of the help message on a per-buffer
+basis, you must use @code{ediff-startup-hook} to change the value of
+the variable @code{ediff-help-message}, which is local to
+@code{ediff-control-buffer}.
+
+@node Window and Frame Configuration, Selective Browsing, Quick Help, Customization
+@section Window and Frame Configuration
+
+On a non-windowing display, Ediff sets things up in one frame, splitting
+it between a small control window and the windows for buffers A, B, and C.
+The split between these windows can be horizontal or
+vertical, which can be changed interactively by typing @kbd{|} while the
+cursor is in the control window.
+
+On a window display, Ediff sets up a dedicated frame for Ediff Control
+Panel and then it chooses windows as follows: If one of the buffers
+is invisible, it is displayed in the currently selected frame.  If
+a buffer is visible, it is displayed in the frame where it is visible.
+If, according to the above criteria, the two buffers fall into the same
+frame, then so be it---the frame will be shared by the two.  The same
+algorithm works when you type @kbd{C-l} (@code{ediff-recenter}), @kbd{p}
+(@code{ediff-previous-difference}), @kbd{n}
+(@code{ediff-next-difference}), etc.
+
+The above behavior also depends on whether the current frame is splittable,
+dedicated, etc. Unfortunately, the margin is too small to present this
+remarkable algorithm.
+
+The bottom line of all this is that you can compare buffers in one frame or
+in different frames.  The former is done by default, while the latter can
+be achieved by arranging buffers A, B (and C, if applicable) to be seen in
+different frames.  Ediff respects these arrangements, automatically
+adapting itself to the multi-frame mode.
+
+Ediff uses the following variables to set up its control panel
+(a.k.a. control buffer, a.k.a. quick help window):
+
+@table @code
+@item ediff-control-frame-parameters
+@vindex ediff-control-frame-parameters
+You can change or augment this variable including the font, color,
+etc.  The X resource name of Ediff Control Panel frames is @samp{Ediff}.  Under
+X-windows, you can use this name to set up preferences in your
+@file{~/.Xdefaults}, @file{~/.xrdb}, or whatever X resource file is in
+use. Usually this is preferable to changing
+@code{ediff-control-frame-parameters} directly.  For instance, you can
+specify in @file{~/.Xdefaults} the color of the control frame
+using the resource @samp{Ediff*background}.
+
+In general, any X resource pertaining the control frame can be reached
+via the prefix @code{Ediff*}.
+
+@item ediff-control-frame-position-function
+@vindex ediff-control-frame-position-function
+The preferred way of specifying the position of the control frame is by
+setting the variable @code{ediff-control-frame-position-function} to an
+appropriate function.
+The default value of this variable is
+@code{ediff-make-frame-position}. This function places the control frame in
+the vicinity of the North-East corner of the frame displaying buffer A.
+
+@findex ediff-make-frame-position
+@end table
+
+The following variables can be used to adjust the location produced by
+@code{ediff-make-frame-position} and for related customization.
+
+@table @code
+@item ediff-narrow-control-frame-leftward-shift
+@vindex ediff-narrow-control-frame-leftward-shift
+Specifies the number of characters for shifting
+the control frame from the rightmost edge of frame A when the control
+frame is displayed as a small window. 
+
+@item ediff-wide-control-frame-rightward-shift
+@vindex ediff-wide-control-frame-rightward-shift
+Specifies the rightward shift of the control frame
+from the left edge of frame A when the control frame shows the full
+menu of options.
+
+@item ediff-control-frame-upward-shift
+@vindex ediff-control-frame-upward-shift
+Specifies the number of pixels for the upward shift
+of the control frame.
+
+@item ediff-prefer-iconified-control-frame
+@vindex ediff-prefer-iconified-control-frame
+If this variable is @code{t}, the control frame becomes iconified
+automatically when you toggle the quick help message off.  This saves
+valuable real estate on the screen.  Toggling help back will deiconify
+the control frame.
+
+To start Ediff with an iconified Control Panel, you should set this
+variable to @code{t} and @code{ediff-prefer-long-help-message} to
+@code{nil} (@pxref{Quick Help}).  This behavior is useful only if the
+window manager is TWM or a derivative. Also, this doesn't work under
+XEmacs, since this editor ignores input from icons.
+@end table
+
+@findex ediff-setup-windows
+To make more creative changes in the way Ediff sets up windows, you can
+rewrite the function @code{ediff-setup-windows}.  However, we believe
+that detaching Ediff Control Panel from the rest and making it into a
+separate frame offers an important opportunity by allowing you to
+iconify that frame.  Under Emacs, the icon will usually accept all of
+the Ediff commands, but will free up valuable real estate on your screen
+(this may depend on the window manager, though).  Iconifying won't do
+any good under XEmacs since XEmacs icons are not sensitive to keyboard
+input.  The saving grace is that, even if not iconified, the control
+frame is very small, smaller than some icons, so it does not take much
+space in any case.
+
+The following variable controls how windows are set up:
+
+@table @code
+@item ediff-window-setup-function
+@vindex ediff-window-setup-function
+The multiframe setup is done by the
+@code{ediff-setup-windows-multiframe} function, which is the default on
+windowing displays.  The plain setup, one where all windows are always
+in one frame, is done by @code{ediff-setup-windows-plain}, which is the
+default on a non-windowing display (or in an xterm window).  In fact,
+under Emacs, you can switch freely between these two setups by executing
+the command @code{ediff-toggle-multiframe} using the Minibuffer.
+@findex ediff-setup-windows-multiframe
+@findex ediff-setup-windows-plain
+@findex ediff-toggle-multiframe
+
+If you don't like any of these setups, write your own function.  See the
+documentation for @code{ediff-window-setup-function} for the basic
+guidelines.  However, writing window setups is not easy, so you should
+first take a close look at @code{ediff-setup-windows-plain} and
+@code{ediff-setup-windows-multiframe}.
+@end table
+
+You can run multiple Ediff sessions at once, by invoking Ediff several
+times without exiting previous Ediff sessions.  Different sessions
+may even operate on the same pair of files.
+
+Each session has its own Ediff Control Panel and all the regarding a
+particular session is local to the associated control panel buffer.  You
+can switch between sessions by suspending one session and then switching
+to another control panel.  (Different control panel buffers are
+distinguished by a numerical suffix, e.g., @samp{Ediff Control Panel<3>}.)
+
+@node Selective Browsing, Highlighting Difference Regions, Window and Frame Configuration, Customization
+@section Selective Browsing
+
+Sometimes it is convenient to be able to step through only some difference
+regions, those that satisfy certain regular expressions, and to ignore all
+others.  On other occasions, you may want to ignore difference regions that
+satisfy some regular expressions, and to look only at the rest.
+
+The commands @kbd{#f} and @kbd{#h} let you do precisely this.
+
+Typing @kbd{#f} lets you specify regular expressions that match difference
+regions you want to focus on.
+We shall call these regular expressions @var{regexp-A}, @var{regexp-B} and
+@var{regexp-C}.
+Ediff will then start stepping through only those difference regions
+where the region in buffer A matches @var{regexp-A} and/or the region in
+buffer B matches @var{regexp-B}, etc.  Whether `and' or `or' will be used
+depends on how you respond to a question.
+
+When scanning difference regions for the aforesaid regular expressions,
+Ediff narrows the buffers to those regions. This means that you can use
+the expressions @kbd{\`} and @kbd{\'} to tie search to the beginning or end
+of the difference regions.
+
+On the other hand, typing @kbd{#h} lets you specify (hide) uninteresting
+regions. That is, if a difference region in buffer A matches
+@var{regexp-A}, the corresponding region in buffer B matches @var{regexp-B}
+and (if applicable) buffer-C's region matches @var{regexp-C}, then the
+region will be ignored by the commands @kbd{n}/@key{SPC}
+(@code{ediff-next-difference}) and @kbd{p}/@key{DEL}
+(@code{ediff-previous-difference}) commands.
+
+Typing @kbd{#f} and @kbd{#h} toggles selective browsing on and off.
+
+Note that selective browsing affects only @code{ediff-next-difference}
+and @code{ediff-previous-difference}, i.e., the commands
+@kbd{n}/@key{SPC} and @kbd{p}/@key{DEL}.  @kbd{#f} and @kbd{#h} do not
+change the position of the point in the buffers.  And you can still jump
+directly (using @kbd{j})  to any numbered
+difference.
+
+Users can supply their own functions to specify how Ediff should do
+selective browsing. To change the default Ediff function, add a function to
+@code{ediff-load-hook} which will do the following assignments:
+
+@example
+(setq ediff-hide-regexp-matches-function 'your-hide-function) 
+(setq ediff-focus-on-regexp-matches-function 'your-focus-function)
+@end example
+
+@strong{Useful hint}: To specify a regexp that matches everything, don't
+simply type @key{RET} in response to a prompt. Typing @key{RET} tells Ediff
+to accept the default value, which may not be what you want. Instead, you
+should enter something like @key{^} or @key{$}. These match every
+line.
+
+You can use the status command, @kbd{i}, to find out whether
+selective browsing is currently in use.
+
+The regular expressions you specified are kept in the local variables
+@code{ediff-regexp-focus-A}, @code{ediff-regexp-focus-B},
+@code{ediff-regexp-focus-C}, @code{ediff-regexp-hide-A},
+@code{ediff-regexp-hide-B}, @code{ediff-regexp-hide-C}. Their default value
+is the empty string (i.e., nothing is hidden or focused on).  To change the
+default, set these variables in @file{.emacs} using @code{setq-default}.
+
+In addition to the ability to ignore regions that match regular
+expressions, Ediff can be ordered to start skipping over certain
+``inessential'' regions.  This is controlled by the following variable:
+
+@table @code
+@item ediff-ignore-similar-regions
+@vindex ediff-ignore-similar-regions
+If @code{t}, causes Ediff to skip over difference regions
+that deemed inessential, i.e., where the only differences are those
+in the white space and newlines.
+@end table
+
+@strong{Note:} In order for this feature to work, auto-refining of
+difference regions must be on, since otherwise Ediff won't know if there
+are fine differences between regions.  On devices where Emacs can display
+faces, auto-refining is a default, but it is not turned on by default on
+text-only terminals.  In that case, you must explicitly turn auto-refining
+on (such as, by typing @kbd{@@}).
+
+@strong{Reassurance:} If many inessential regions appear in a row, Ediff may
+take a long time to jump to the next region because it has to compute
+fine differences of all intermediate regions.  This delay does not
+indicate any problem.
+
+@node Highlighting Difference Regions, Narrowing, Selective Browsing, Customization
+@section Highlighting Difference Regions
+
+The following variables control the way Ediff highlights difference
+regions:
+
+@table @code
+@item ediff-before-flag-bol
+@itemx ediff-after-flag-eol
+@itemx ediff-before-flag-mol
+@itemx ediff-after-flag-mol
+@vindex ediff-before-flag-bol
+@vindex ediff-after-flag-eol
+@vindex ediff-before-flag-mol
+@vindex ediff-after-flag-mol
+These variables hold strings that Ediff uses to mark the beginning and the
+end of the differences found in files A, B, and C on devices where Emacs
+cannot display faces. Ediff uses different flags to highlight regions that
+begin/end at the beginning/end of a line or in a middle of a line.
+
+@item ediff-current-diff-face-A
+@itemx ediff-current-diff-face-B
+@itemx ediff-current-diff-face-C
+@vindex ediff-current-diff-face-A
+@vindex ediff-current-diff-face-B
+@vindex ediff-current-diff-face-C
+Ediff uses these faces to highlight current differences on devices where
+Emacs can display faces.  These and subsequently described faces can be set
+either in @file{.emacs} or in @file{.Xdefaults}. The X resource for Ediff
+is @samp{Ediff}, @emph{not} @samp{emacs}. Please refer to Emacs manual for
+the information on how to set X resources.
+@item ediff-fine-diff-face-A
+@itemx ediff-fine-diff-face-B
+@itemx ediff-fine-diff-face-C
+@vindex ediff-fine-diff-face-A
+@vindex ediff-fine-diff-face-B
+@vindex ediff-fine-diff-face-C
+Ediff uses these faces to show the fine differences between the current
+differences regions in buffers A, B, and C, respectively.
+
+@item ediff-even-diff-face-A
+@itemx ediff-even-diff-face-B
+@itemx ediff-even-diff-face-C
+@itemx ediff-odd-diff-face-A
+@itemx ediff-odd-diff-face-B
+@itemx ediff-odd-diff-face-C
+@vindex ediff-even-diff-face-A
+@vindex ediff-even-diff-face-B
+@vindex ediff-even-diff-face-C
+@vindex ediff-odd-diff-face-A
+@vindex ediff-odd-diff-face-B
+@vindex ediff-odd-diff-face-C
+Non-current difference regions are displayed using these alternating
+faces. The odd and the even faces are actually identical on monochrome
+displays, because without colors options are limited.
+So, Ediff uses italics to highlight non-current differences.
+
+@item ediff-force-faces
+@vindex ediff-force-faces
+Ediff generally can detect when Emacs is running on a device where it can
+use highlighting with faces. However, if it fails to determine that faces
+can be used, the user can set this variable to @code{t} to make sure that
+Ediff uses faces to highlight differences.
+
+@item ediff-highlight-all-diffs
+@vindex ediff-highlight-all-diffs
+Indicates whether---on a window system---Ediff should highlight differences
+using inserted strings (as on a text-only terminal) or using colors and
+highlighting.  Normally, Ediff highlights all differences, but the
+selected difference is highlighted more visibly.  One can cycle through
+various modes of highlighting by typing @kbd{h}.  By default, Ediff
+starts in the mode where all difference regions are highlighted.  If you
+prefer to start in the mode where unselected differences are not
+highlighted, you should set @code{ediff-highlight-all-diffs} to
+@code{nil}.  Type @kbd{h} to restore highlighting of all differences.
+
+Ediff lets you switch between the two modes of highlighting.  That is,
+you can switch interactively from highlighting using faces to
+highlighting using string flags, and back.  Of course, switching has
+effect only under a windowing system.  On a text-only terminal or in an
+xterm window, the only available option is highlighting with strings.
+@end table
+
+@noindent
+If you want to change the above variables, you must do it
+@strong{before} Ediff is loaded. 
+
+There are two ways to change the default setting
+for highlighting faces: either change the variables, as shown here,
+
+@example
+(setq ediff-current-diff-face-A 'bold-italic)
+@end example
+
+@noindent
+or here,
+
+@example
+(setq ediff-current-diff-face-A
+(copy-face 'bold-italic 'ediff-current-diff-face-A))
+@end example
+
+@noindent
+or modify the defaults selectively:
+
+@smallexample
+(add-hook 'ediff-load-hook
+          (function (lambda () 
+                      (set-face-foreground
+                        ediff-current-diff-face-B "blue")
+                      (set-face-background
+                        ediff-current-diff-face-B "red")
+                      (make-face-italic
+                        ediff-current-diff-face-B))))
+@end smallexample
+
+You may also want to take a look at how the above faces are defined in the
+source code of Ediff. 
+
+@strong{Note:} it is not recommended to use @code{internal-get-face} (or
+@code{get-face} in XEmacs) when defining Ediff's faces, since this may
+cause problems when there are several frames with different font sizes.
+Instead, use @code{copy-face} or @code{set/make-face-@dots{}} as shown
+above.
+
+@node Narrowing, Refinement of Difference Regions, Highlighting Difference Regions, Customization
+@section Narrowing
+
+If buffers being compared are narrowed at the time of invocation of
+Ediff, @code{ediff-buffers} will preserve the narrowing range.  However,
+if @code{ediff-files} is invoked on the files visited by these buffers,
+that widens the buffers, since this command is defined to compare the
+entire files.
+
+Calling @code{ediff-regions-linewise} or @code{ediff-windows-linewise},
+or the corresponding @samp{-wordwise} commands, narrows the buffers
+being compared (corresponding to the regions being compared).  The
+original accessible ranges are restored when you quit Ediff.
+During the command, you can toggle this narrowing on and off
+with the @kbd{%} command.
+
+These two variables control this narrowing behavior:
+
+@table @code
+@item ediff-start-narrowed
+@vindex ediff-start-narrowed
+If @code{t}, Ediff narrows the display to the appropriate range when it
+is invoked with an @samp{ediff-regions@dots{}} or
+@samp{ediff-windows@dots{}} command.  If @code{nil}, these commands do
+not automatically narrow, but you can still toggle narrowing on and off
+by typing @kbd{%}.
+
+@item ediff-quit-widened
+@vindex ediff-quit-widened
+Controls whether on quitting Ediff should restore the accessible range
+that existed before the current invocation.
+@end table
+
+@node Refinement of Difference Regions, Patch and Diff Programs, Narrowing, Customization
+@section Refinement of Difference Regions
+
+Ediff has variables to control the way fine differences are
+highlighted.  This feature gives you control over the process of refinement.
+Note that refinement ignores spaces, tabs, and newlines.
+
+@table @code
+@item ediff-auto-refine
+@vindex ediff-auto-refine
+This variable controls whether fine differences within regions are
+highlighted automatically (``auto-refining'').  The default is yes
+(@samp{on}).
+
+On a slow machine, automatic refinement may be painful.  In that case,
+you can turn auto-refining on or off interactively by typing
+@kbd{@@}.  You can also turn off display of refining that has
+already been done.
+
+When auto-refining is off, fine differences are shown only for regions
+for which these differences have been computed and saved before.  If
+auto-refining and display of refining are both turned off, fine
+differences are not shown at all.
+
+Typing @kbd{*} computes and displays fine differences for the current
+difference region, regardless of whether auto-refining is turned on.
+
+@item ediff-auto-refine-limit
+@vindex ediff-auto-refine-limit
+If auto-refining is on, this variable limits the size of the regions to
+be auto-refined.  This guards against the possible slowdown that may be
+caused by extraordinary large difference regions.
+
+You can always refine the current region by typing @kbd{*}.
+
+@item ediff-forward-word-function
+@vindex ediff-forward-word-function
+This variable gives control over how fine differences are computed.  The
+value must be a Lisp function that determines how the current difference
+region should be split into words.
+
+@vindex ediff-diff-program
+@vindex ediff-forward-word-function
+@findex ediff-forward-word
+Fine differences are computed by first splitting the current difference
+region into words and then passing this along to
+@code{ediff-diff-program}. For the default
+@code{ediff-forward-word-function} (which is @code{ediff-forward-word}), a
+word is a string consisting of letters, @samp{-}, or @samp{_}; a string of
+punctuation symbols; a string of digits, or a string consisting of symbols
+that are neither space, nor a letter.
+
+This default behavior is controlled by four variables: @code{ediff-word-1},
+..., @code{ediff-word-4}. See the on-line documentation for these variables
+and for the function @code{ediff-forward-word} for an explanation of how to
+modify these variables.
+@vindex ediff-word-1
+@vindex ediff-word-2
+@vindex ediff-word-3
+@vindex ediff-word-4
+@end table
+
+Sometimes, when a region has too many differences between the variants,
+highlighting of fine differences is inconvenient, especially on
+color displays.  If that is the case, type @kbd{*} with a negative
+prefix argument.  This unhighlights fine differences for the current
+region.
+
+To unhighlight fine differences in all difference regions, use the
+command @kbd{@@}.  Repeated typing of this key cycles through three
+different states: auto-refining, no-auto-refining, and no-highlighting
+of fine differences.
+
+@node Patch and Diff Programs, Merging and diff3, Refinement of Difference Regions, Customization
+@section Patch and Diff Programs
+
+This section describes variables that specify the programs to be used for
+applying patches and for computing the main difference regions (not the
+fine difference regions):
+
+@table @code
+@item ediff-patch-program
+@itemx ediff-diff-program
+@itemx ediff-diff3-program
+@vindex ediff-patch-program
+@vindex ediff-diff-program
+@vindex ediff-diff3-program
+These variables specify the programs to use to produce differences
+and do patching.
+
+@item ediff-patch-options
+@itemx ediff-diff-options
+@itemx ediff-diff3-options
+@vindex ediff-patch-options
+@vindex ediff-diff-options
+@vindex ediff-diff3-options
+These variables specify the options to pass to the above utilities.
+
+In @code{ediff-diff-options}, it may be useful to specify options
+such as @samp{-w} that ignore certain kinds of changes.  However,
+Ediff does not let you use the option @samp{-c}, as it doesn't recognize this
+format yet.
+
+
+@item ediff-custom-diff-program
+@itemx ediff-custom-diff-options
+@vindex ediff-custom-diff-program
+@vindex ediff-custom-diff-options
+@findex ediff-save-buffer
+Because Ediff limits the options you may want to pass to the @code{diff}
+program, it partially makes up for this drawback by letting you save the
+output from @code{diff} in your preferred format, which is specified via
+the above two variables.
+
+The output generated by @code{ediff-custom-diff-program} (which doesn't
+even have to be a standard-style @file{diff}!) is not used by Ediff. It is
+provided exclusively so that you can
+refer to
+it later, send it over email, etc.  For instance, after reviewing the
+differences, you may want to send context differences to a colleague.
+Since Ediff ignores the @samp{-c} option in
+@code{ediff-diff-program}, you would have to run @code{diff -c} separately
+just to produce the list of differences. Fortunately,
+@code{ediff-custom-diff-program} and @code{ediff-custom-diff-options}
+eliminate this nuisance by keeping a copy of a difference list in the
+desired format in a buffer that can be displayed via the command @kbd{D}.
+
+@item ediff-patch-default-directory
+@vindex ediff-patch-default-directory
+Specifies the default directory to look for patches.
+
+@end table
+
+@noindent
+@strong{Warning:} Ediff does not support the output format of VMS
+@code{diff}.  Instead, make sure to use some implementation of POSIX
+@code{diff}, such as @code{gnudiff}.
+
+@node Merging and diff3, Support for Version Control, Patch and Diff Programs, Customization
+@section Merging and diff3
+
+Ediff supports three-way comparison via the functions @code{ediff-files3} and
+@code{ediff-buffers3}.  The interface is the same as for two-way comparison.
+In three-way comparison and merging, Ediff reports if any two difference
+regions are identical.  For instance, if the current region in buffer A
+is the same as the region in buffer C, then the mode line of buffer A will
+display @samp{[=diff(C)]} and the mode line of buffer C will display
+@samp{[=diff(A)]}. 
+
+Merging is done according to the following algorithm.
+
+If a difference region in one of the buffers, say B, differs from the ancestor
+file while the region in the other buffer, A, doesn't, then the merge buffer,
+C, gets B's region.  Similarly when buffer A's region differs from
+the ancestor and B's doesn't, A's region is used.
+
+@vindex ediff-default-variant
+If both regions in buffers A and B differ from the ancestor file, Ediff
+chooses the region according to the value of the variable
+@code{ediff-default-variant}.  If its value is @code{default-A} then A's
+region is chosen.  If it is @code{default-B} then B's region is chosen.
+If it is @code{combined} then the region in buffer C will look like
+this:
+
+@example
+#ifdef NEW  /* variant A */
+difference region from buffer A
+#else  /* variant B */
+difference region from buffer B
+#endif  /* NEW */
+@end example
+
+@vindex ediff-combination-pattern
+The actual strings that separate the regions copied from buffer A and B
+are controlled by the variable @code{ediff-combination-pattern}.  Its
+value should be a list of three strings.  The first is inserted before
+the difference region of buffer A; the second string goes between the
+regions; the third goes after region B, as shown in the above example.
+
+In addition to the state of the difference, during merging Ediff
+displays the state of the merge for each region. If a difference came
+from buffer A by default (because both regions A and B were different
+from the ancestor and @code{ediff-default-variant} was set to @code{default-A})
+then @samp{[=diff(A) default-A]} is displayed in the mode line.  If the
+difference in buffer C came, say, from buffer B because the difference region
+in that buffer differs from the ancestor, but the region in buffer A
+does not (if merging with an ancestor) then @samp{[=diff(B) prefer-B]} is
+displayed.  The indicators default-A/B and prefer-A/B are inspired by
+Emerge and have the same meaning. 
+
+Another indicator of the state of merge is @samp{combined}.  It appears
+with any difference region in buffer C that was obtained by combining
+the difference regions in buffers A and B as explained above.
+
+In addition to state of merge and difference indicator, while merging with an
+ancestor file or buffer, Ediff informs the user when the current difference
+region in the (normally invisible) ancestor buffer is empty via the
+@emph{AncestorEmpty} indicator. This helps determine if the changes
+made to the original in variants A and B represent pure insertion or
+deletion of text: if the mode line shows @emph{AncestorEmpty} and the
+corresponding region in buffers A or B is not empty, this means that new
+text was inserted. If this indicator is not present and the difference
+regions in buffers A or B are non-empty, this means that text was
+modified. Otherwise, the original text was deleted.
+
+Although the ancestor buffer is normally invisible, Ediff maintains
+difference regions there and advances the current difference region
+accordingly. All highlighting of difference regions is provided in the
+ancestor buffer, except for the fine differences.  Therefore, if desired, the
+user can put the ancestor buffer in a separate frame and watch it
+there. However, on a TTY, only one frame can be visible at any given time,
+and Ediff doesn't support any single-frame window configuration where all
+buffers, including the ancestor buffer, would be visible. However, the
+ancestor buffer can be displayed by typing @kbd{/} to the control
+window. (Type @kbd{C-l} to hide it again.)
+
+Note that the state-of-difference indicators @samp{=diff(A)} and
+@samp{=diff(B)} above are not redundant, even in the presence of a
+state-of-merge indicator.  In fact, the two serve different purposes.
+
+For instance, if the mode line displays @samp{=diff(B) prefer(B)} and
+you copy a difference region from buffer A to buffer C then
+@samp{=diff(B)} will change to @samp{diff-A} and the mode line will
+display @samp{=diff(A) prefer-B}.  This indicates that the difference
+region in buffer C is identical to that in buffer A, but originally
+buffer C's region came from buffer B.  This is useful to know because
+you can recover the original difference region in buffer C by typing
+@kbd{r}.
+
+
+Ediff never changes the state-of-merge indicator, except in response to
+the @kbd{!} command (see below), in which case the indicator is lost.
+On the other hand, the state-of-difference indicator is changed
+automatically by the copying/recovery commands, @kbd{a}, @kbd{b}, @kbd{r},
+@kbd{+}. 
+
+The @kbd{!} command loses the information about origins of the regions
+in the merge buffer (default-A, prefer-B, or combined).  This is because
+recomputing differences in this case means running @code{diff3} on
+buffers A, B, and the merge buffer, not on the ancestor buffer.  (It
+makes no sense to recompute differences using the ancestor file, since
+in the merging mode Ediff assumes that you have not edited buffers A and
+B, but that you may have edited buffer C, and these changes are to be
+preserved.)  Since some difference regions may disappear as a result of
+editing buffer C and others may arise, there is generally no simple way
+to tell where the various regions in the merge buffer came from.
+
+In three-way comparison, Ediff tries to disregard regions that consist
+entirely of white space.  For instance, if, say, the current region in
+buffer A consists of the white space only (or if it is empty), Ediff will
+not take it into account for the purpose of computing fine differences. The
+result is that Ediff can provide a better visual information regarding the
+actual fine differences in the non-white regions in buffers B and
+C. Moreover, if the regions in buffers B and C differ in the white space
+only, then a message to this effect will be displayed.
+
+@vindex ediff-merge-window-share
+In the merge mode, the share of the split between window C (the window
+displaying the merge-buffer) and the windows displaying buffers A and B
+is controlled by the variable @code{ediff-merge-window-share}.  Its
+default value is 0.5.  To make the merge-buffer window smaller, reduce
+this amount.
+
+We don't recommend increasing the size of the merge-window to more than
+half the frame (i.e., to increase the value of
+@code{ediff-merge-window-share}) to more than 0.5, since it would be
+hard to see the contents of buffers A and B.
+
+You can temporarily shrink the merge window to just one line by
+typing @kbd{s}.  This change is temporary, until Ediff finds a reason to
+redraw the screen.  Typing @kbd{s} again restores the original window size.
+
+With a positive prefix argument, the @kbd{s} command will make the merge
+window slightly taller.  This change is persistent.  With `@kbd{-}' or
+with a negative prefix argument, the command @kbd{s} makes the merge
+window slightly shorter.  This change also persistent.
+
+@vindex ediff-show-clashes-only
+Ediff lets you automatically ignore the regions where only one of the
+buffers A and B disagrees with the ancestor.  To do this, set the
+variable @code{ediff-show-clashes-only} to non-@code{nil}.
+
+You can toggle this feature interactively by typing @kbd{$}.
+
+Note that this variable controls only how Ediff chooses the
+next/previous difference to show.  You can still jump directly to any
+difference using the command @kbd{j} (with a prefix argument specifying
+the difference number).
+
+@node Support for Version Control, Customizing the Mode Line, Merging and diff3, Customization
+@section Support for Version Control
+
+
+Ediff supports version control and lets you compare versions of files
+visited by Emacs buffers via the function @code{ediff-revision}. This
+feature is controlled by the following variables:
+
+@table @code
+@item ediff-version-control-package
+@vindex ediff-version-control-package
+A symbol. The default is @samp{vc}.
+
+If you are like most Emacs users, Ediff will use VC as the version control
+package. This is the standard Emacs interface to RCS, CVS, and SCCS.
+
+However, if your needs are better served by other interfaces, you will
+have to tell Ediff which version control package you are using, e.g.,
+@example
+(setq ediff-version-control-package 'rcs)
+@end example
+
+Apart from the standard @file{vc.el}, Ediff supports three other interfaces
+to version control:
+@file{rcs.el}, @file{pcl-cvs.el}, and @file{generic-sc.el}. 
+The package @file{rcs.el} is written by Sebastian Kremer
+<sk@@thp.Uni-Koeln.DE> and is available as
+@example
+@file{ftp.cs.buffalo.edu:pub/Emacs/rcs.tar.Z}
+@file{ftp.uni-koeln.de:/pub/gnu/emacs/rcs.tar.Z}
+@end example
+The packages @file{pcl-cvs.el} and @file{generic-sc.el} are found in XEmacs
+distribution.
+@pindex @file{vc.el}
+@pindex @file{rcs.el}
+@pindex @file{pcl-cvs.el}
+@pindex @file{generic-sc.el}
+@end table
+
+Ediff's interface to the above packages allows the user to compare the
+versions of the current buffer or to merge them (with or without an
+ancestor-version). These operations can also be performed on directories
+containing files under version control.
+
+In case of @file{pcl-cvs.el}, Ediff can also be invoked via the function
+@code{run-ediff-from-cvs-buffer}---see the documentation string for this
+function.
+
+@node Customizing the Mode Line, Miscellaneous, Support for Version Control, Customization
+@section Customizing the Mode Line
+
+When Ediff is running, the mode line of @samp{Ediff Control Panel}
+buffer shows the current difference number and the total number of
+difference regions in the two files.
+
+The mode line of the buffers being compared displays the type of the
+buffer (@samp{A:}, @samp{B:}, or @samp{C:}) and (usually) the file name.
+Ediff tries to be intelligent in choosing the mode line buffer
+identification.  In particular, it works well with the
+@file{uniquify.el} and @file{mode-line.el} packages (which improve on
+the default way in which Emacs displays buffer identification).  If you
+don't like the way Ediff changes the mode line, you can use
+@code{ediff-prepare-buffer-hook} to modify the mode line.
+@vindex ediff-prepare-buffer-hook
+@pindex @file{uniquify.el}
+@pindex @file{mode-line.el}
+
+@node Miscellaneous, Notes on Heavy-duty Customization, Customizing the Mode Line, Customization
+@section Miscellaneous
+
+Here are a few other variables for customizing Ediff:
+
+@table @code
+@item ediff-split-window-function
+@vindex ediff-split-window-function
+Controls the way you want the window be split between file-A and file-B
+(and file-C, if applicable).  It defaults to the vertical split
+(@code{split-window-vertically}, but you can set it to
+@code{split-window-horizontally}, if you so wish.
+Ediff also lets you switch from vertical to horizontal split and back
+interactively.
+
+Note that if Ediff detects that all the buffers it compares are displayed in
+separate frames, it assumes that the user wants them to be so displayed
+and stops splitting windows.  Instead, it arranges for each buffer to
+be displayed in a separate frame. You can switch to the one-frame mode
+by hiding one of the buffers A/B/C.
+
+You can also swap the windows where buffers are displayed by typing
+@kbd{~}.
+
+@item ediff-merge-split-window-function
+@vindex ediff-merge-split-window-function
+Controls how windows are
+split between buffers A and B in the merge mode.
+This variable is like @code{ediff-split-window-function}, but it defaults
+to @code{split-window-horizontally} instead of
+@code{split-window-vertically}.
+
+@item ediff-make-wide-display-function
+@vindex ediff-make-wide-display-function
+The value is a function to be called to widen the frame for displaying
+the Ediff buffers.  See the on-line documentation for
+@code{ediff-make-wide-display-function} for details.  It is also
+recommended to look into the source of the default function
+@code{ediff-make-wide-display}.
+
+You can toggle wide/regular display by typing @kbd{m}.  In the wide
+display mode, buffers A, B (and C, when applicable) are displayed in a
+single frame that is as wide as the entire workstation screen.  This is
+useful when files are compared side-by-side.  By default, the display is
+widened without changing its height.
+
+@item ediff-use-last-dir
+@vindex ediff-use-last-dir
+Controls the way Ediff presents the
+default directory when it prompts the user for files to compare.  If
+@code{nil},
+Ediff uses the default directory of the current buffer when it
+prompts the user for file names.  Otherwise, it will use the
+directories it had previously used for files A, B, or C, respectively.
+
+@item ediff-no-emacs-help-in-control-buffer
+@vindex ediff-no-emacs-help-in-control-buffer
+If @code{t}, makes @kbd{C-h}
+behave like the @key{DEL} key, i.e., it will move you back to the previous
+difference rather than invoking help.  This is useful when, in an xterm
+window or a text-only terminal, the Backspace key is bound to @kbd{C-h} and is
+positioned more conveniently than the @key{DEL} key.
+
+@item ediff-toggle-read-only-function
+@vindex ediff-toggle-read-only-function
+This variable's value is a function that Ediff uses to toggle
+the read-only property in its buffers.
+
+The default function that Ediff uses simply toggles the read-only property,
+unless the file is under version control.  For a checked-in file under
+version control, Ediff first tries to check the file out.
+
+@item ediff-keep-variants
+@vindex @code{ediff-keep-variants}
+The default is @code{t}, meaning that the buffers being compared or merged will
+be preserved when Ediff quits. Setting this to @code{nil} causes Ediff to
+offer the user a chance to delete these buffers (if they are not modified).
+Supplying a prefix argument to the quit command (@code{q}) temporarily
+reverses the meaning of this variable. This is convenient when the user
+prefers one of the behaviors most of the time, but occasionally needs the
+other behavior.
+
+However, Ediff temporarily resets this variable to @code{t} if it is
+invoked via one of the "buffer" jobs, such as @code{ediff-buffers}.
+This is because it is all too easy to loose day's work otherwise.
+Besides, in a "buffer" job, the variant buffers have already been loaded
+prior to starting Ediff, so Ediff just preserves status quo here.
+
+Using @code{ediff-cleanup-hook}, one can make Ediff delete the variants
+unconditionally (e.g., by making @code{ediff-janitor} into one of these hooks).
+@item ediff-grab-mouse
+@vindex @code{ediff-grab-mouse}
+Default is @code{t}.  Normally, Ediff grabs mouse and puts it in its
+control frame.  This is useful since the user can be sure that when he
+needs to type an Ediff command the focus will be in an appropriate Ediff's
+frame.  However, some users prefer to move the mouse by themselves.  The
+above variable, if set to @code{maybe}, will prevent Ediff from grabbing
+the mouse in many situations, usually after commands that may take more
+time than usual. In other situation, Ediff will continue grabbing the mouse
+and putting it where it believes is appropriate.  If the value is
+@code{nil}, then mouse is entirely user's responsibility.
+Try different settings and see which one is for you.
+@end table
+
+
+@node Notes on Heavy-duty Customization, , Miscellaneous, Customization
+@section Notes on Heavy-duty Customization
+
+Some users need to customize Ediff in rather sophisticated ways, which
+requires different defaults for different kinds of files (e.g., SGML,
+etc.).  Ediff supports this kind of customization in several ways.  First,
+most customization variables are buffer-local. Those that aren't are
+usually accessible from within Ediff Control Panel, so one can make them
+local to the panel by calling make-local-variable from within
+@code{ediff-startup-hook}. 
+
+Second, the function @code{ediff-setup} accepts an optional sixth
+argument which has the form @code{((@var{var-name-1} . @var{val-1})
+(@var{var-name-2} . @var{val-2}) @dots{})}.  The function
+@code{ediff-setup} sets the variables in the list to the respective
+values, locally in the Ediff control buffer.  This is an easy way to
+throw in custom variables (which usually should be buffer-local) that
+can then be tested in various hooks.
+
+Make sure the variable @code{ediff-job-name} and @code{ediff-word-mode} are set
+properly in this case, as some things in Ediff depend on this.
+
+Finally, if you want custom-tailored help messages, you can set the
+variables @code{ediff-brief-help-message-function} and
+@code{ediff-long-help-message-function}
+to functions that return help strings.
+@vindex ediff-startup-hook
+@findex ediff-setup
+@vindex ediff-job-name
+@vindex ediff-word-mode
+@vindex ediff-brief-help-message-function
+@vindex ediff-long-help-message-function
+
+When customizing Ediff, some other variables are useful, although they are
+not user-definable. They are local to the Ediff control buffer, so this
+buffer must be current when you access these variables. The control buffer
+is accessible via the variable @code{ediff-control-buffer}, which is also
+local to that buffer. It is usually used for checking if the current buffer
+is also the control buffer.
+
+Other variables of interest are:
+@table @code
+@item ediff-buffer-A
+The first of the data buffers being compared.
+
+@item ediff-buffer-B
+The second of the data buffers being compared.
+
+@item ediff-buffer-C
+In three-way comparisons, this is the third buffer being compared.
+In merging, this is the merge buffer.
+In two-way comparison, this variable is nil.
+
+@item ediff-window-A
+The window displaying buffer A. If buffer A is not visible, this variable
+is nil or it may be a dead window.
+
+@item ediff-window-B
+The window displaying buffer B.
+
+@item ediff-window-C
+The window displaying buffer C, if any.
+
+@item ediff-control-frame
+A dedicated frame displaying the control buffer, if it exists.
+It is non-nil only if Ediff uses the multiframe display, i.e., when the
+control buffer is in its own frame.
+@end table
+
+@node Credits, Index, Customization, Top
+@chapter Credits
+
+Ediff was written by Michael Kifer <kifer@@cs.sunysb.edu>. It was inspired
+by emerge.el written by Dale R. Worley <drw@@math.mit.edu>.  An idea due to
+Boris Goldowsky <boris@@cs.rochester.edu> made it possible to highlight
+fine differences in Ediff buffers. Alastair Burt <burt@@dfki.uni-kl.de>
+ported Ediff to XEmacs, and Eric Freudenthal <freudent@@jan.ultra.nyu.edu>
+made it work with VC.
+
+Many people provided help with bug reports, patches, and advice.
+Without them, Ediff would not be nearly as useful as it is today.
+Here is a full list of contributors (I hope I didn't miss anyone):
+
+@example
+Neal Becker (neal@@ctd.comsat.com),
+Alastair Burt (burt@@dfki.uni-kl.de), Paul Bibilo (peb@@delcam.co.uk),
+Kevin Broadey (KevinB@@bartley.demon.co.uk),
+Harald Boegeholz (hwb@@machnix.mathematik.uni-stuttgart.de),
+Bradley A. Bosch (brad@@lachman.com),
+Michael D. Carney  (carney@@ltx-tr.com),
+Jin S. Choi (jin@@atype.com),
+Albert Dvornik (bert@@mit.edu),
+Eric Eide (eeide@@asylum.cs.utah.edu),
+Kevin Esler (esler@@ch.hp.com), Robert Estes (estes@@ece.ucdavis.edu), 
+Xavier Fornari (xavier@@europe.cma.fr),
+Eric Freudenthal (freudent@@jan.ultra.nyu.edu),
+Job Ganzevoort (Job.Ganzevoort@@cwi.nl),
+Boris Goldowsky (boris@@cs.rochester.edu),
+Allan Gottlieb (gottlieb@@allan.ultra.nyu.edu), Xiaoli Huang (hxl@@epic.com),
+Larry Gouge (larry@@itginc.com), Karl Heuer (kwzh@@gnu.ai.mit.edu),
+(irvine@@lks.csi.com), (jaffe@@chipmunk.cita.utoronto.ca),
+David Karr (dkarr@@nmo.gtegsc.com),
+Norbert Kiesel (norbert@@i3.informatik.rwth-aachen.de),
+Leigh L Klotz (klotz@@adoc.xerox.com), Fritz Knabe (Fritz.Knabe@@ecrc.de),
+Heinz Knutzen (hk@@informatik.uni-kiel.d400.de),
+Andrew Koenig (ark@@research.att.com),
+Ken Laprade (laprade@@dw3f.ess.harris.com), Will C Lauer (wcl@@cadre.com),
+Richard Levitte (levitte@@e.kth.se), Mike Long (mike.long@@analog.com),
+Martin Maechler (maechler@@stat.math.ethz.ch),
+Simon Marshall (Simon.Marshall@@mail.esrin.esa.it),
+Richard Mlynarik (mly@@adoc.xerox.com),
+Chris Murphy (murphycm@@sun.aston.ac.uk),
+Erik Naggum (erik@@naggum.no),
+Eyvind Ness (Eyvind.Ness@@hrp.no), Ray Nickson (nickson@@cs.uq.oz.au), 
+David Petchey (petchey_david@@jpmorgan.com),
+Benjamin Pierce (benjamin.pierce@@cl.cam.ac.uk),
+Tibor Polgar (tlp00@@spg.amdahl.com),
+David Prince (dave0d@@fegs.co.uk),
+Paul Raines (raines@@slac.stanford.edu), 
+C.S. Roberson (roberson@@aur.alcatel.com),
+Kevin Rodgers (kevin.rodgers@@ihs.com),
+Sandy Rutherford (sandy@@ibm550.sissa.it),
+Heribert Schuetz (schuetz@@ecrc.de), Andy Scott (ascott@@pcocd2.intel.com),
+Axel Seibert (axel@@tumbolia.ppp.informatik.uni-muenchen.de),
+Richard Stallman (rms@@gnu.ai.mit.edu), 
+Richard Stanton (stanton@@haas.berkeley.edu), 
+Ake Stenhoff (etxaksf@@aom.ericsson.se), Stig (stig@@hackvan.com),
+Peter Stout (Peter_Stout@@cs.cmu.edu), Chuck Thompson (cthomp@@cs.uiuc.edu),
+Ray Tomlinson (tomlinso@@bbn.com),
+Raymond Toy (toy@@rtp.ericsson.se),
+Ben Wing (wing@@666.com),
+Ilya Zakharevich (ilya@@math.ohio-state.edu),
+Eli Zaretskii (eliz@@is.elta.co.il)
+@end example
+
+@node Index, , Credits, Top
+@unnumbered Index
+@printindex cp
+
+@contents
+@bye