@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
-@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999,
-@c 2003, 2004, 2005 Free Software Foundation, Inc.
+@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2002,
+@c 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@setfilename ../info/modes
@node Modes, Documentation, Keymaps, Top
@ref{Keymaps}, and @ref{Syntax Tables}.
@menu
+* Hooks:: How to use hooks; how to write code that provides hooks.
* Major Modes:: Defining major modes.
* Minor Modes:: Defining minor modes.
* Mode Line Format:: Customizing the text that appears in the mode line.
* Font Lock Mode:: How modes can highlight text according to syntax.
* Desktop Save Mode:: How modes can have buffer state saved between
Emacs sessions.
-* Hooks:: How to use hooks; how to write code that provides hooks.
@end menu
+@node Hooks
+@section Hooks
+@cindex hooks
+
+ A @dfn{hook} is a variable where you can store a function or functions
+to be called on a particular occasion by an existing program. Emacs
+provides hooks for the sake of customization. Most often, hooks are set
+up in the init file (@pxref{Init File}), but Lisp programs can set them also.
+@xref{Standard Hooks}, for a list of standard hook variables.
+
+@cindex normal hook
+ Most of the hooks in Emacs are @dfn{normal hooks}. These variables
+contain lists of functions to be called with no arguments. When the
+hook name ends in @samp{-hook}, that tells you it is normal. We try to
+make all hooks normal, as much as possible, so that you can use them in
+a uniform way.
+
+ Every major mode function is supposed to run a normal hook called the
+@dfn{mode hook} as the last step of initialization. This makes it easy
+for a user to customize the behavior of the mode, by overriding the
+buffer-local variable assignments already made by the mode. Most
+minor modes also run a mode hook at their end. But hooks are used in
+other contexts too. For example, the hook @code{suspend-hook} runs
+just before Emacs suspends itself (@pxref{Suspending Emacs}).
+
+ The recommended way to add a hook function to a normal hook is by
+calling @code{add-hook} (see below). The hook functions may be any of
+the valid kinds of functions that @code{funcall} accepts (@pxref{What
+Is a Function}). Most normal hook variables are initially void;
+@code{add-hook} knows how to deal with this. You can add hooks either
+globally or buffer-locally with @code{add-hook}.
+
+@cindex abnormal hook
+ If the hook variable's name does not end with @samp{-hook}, that
+indicates it is probably an @dfn{abnormal hook}. Then you should look at its
+documentation to see how to use the hook properly.
+
+ If the variable's name ends in @samp{-functions} or @samp{-hooks},
+then the value is a list of functions, but it is abnormal in that either
+these functions are called with arguments or their values are used in
+some way. You can use @code{add-hook} to add a function to the list,
+but you must take care in writing the function. (A few of these
+variables, notably those ending in @samp{-hooks}, are actually
+normal hooks which were named before we established the convention of
+using @samp{-hook} for them.)
+
+ If the variable's name ends in @samp{-function}, then its value
+is just a single function, not a list of functions.
+
+ Here's an example that uses a mode hook to turn on Auto Fill mode when
+in Lisp Interaction mode:
+
+@example
+(add-hook 'lisp-interaction-mode-hook 'turn-on-auto-fill)
+@end example
+
+ At the appropriate time, Emacs uses the @code{run-hooks} function to
+run particular hooks.
+
+@defun run-hooks &rest hookvars
+This function takes one or more normal hook variable names as
+arguments, and runs each hook in turn. Each argument should be a
+symbol that is a normal hook variable. These arguments are processed
+in the order specified.
+
+If a hook variable has a non-@code{nil} value, that value may be a
+function or a list of functions. (The former option is considered
+obsolete.) If the value is a function (either a lambda expression or
+a symbol with a function definition), it is called. If it is a list
+that isn't a function, its elements are called, consecutively. All
+the hook functions are called with no arguments.
+@end defun
+
+@defun run-hook-with-args hook &rest args
+This function is the way to run an abnormal hook and always call all
+of the hook functions. It calls each of the hook functions one by
+one, passing each of them the arguments @var{args}.
+@end defun
+
+@defun run-hook-with-args-until-failure hook &rest args
+This function is the way to run an abnormal hook until one of the hook
+functions fails. It calls each of the hook functions, passing each of
+them the arguments @var{args}, until some hook function returns
+@code{nil}. It then stops and returns @code{nil}. If none of the
+hook functions return @code{nil}, it returns a non-@code{nil} value.
+@end defun
+
+@defun run-hook-with-args-until-success hook &rest args
+This function is the way to run an abnormal hook until a hook function
+succeeds. It calls each of the hook functions, passing each of them
+the arguments @var{args}, until some hook function returns
+non-@code{nil}. Then it stops, and returns whatever was returned by
+the last hook function that was called. If all hook functions return
+@code{nil}, it returns @code{nil} as well.
+@end defun
+
+@defun add-hook hook function &optional append local
+This function is the handy way to add function @var{function} to hook
+variable @var{hook}. You can use it for abnormal hooks as well as for
+normal hooks. @var{function} can be any Lisp function that can accept
+the proper number of arguments for @var{hook}. For example,
+
+@example
+(add-hook 'text-mode-hook 'my-text-hook-function)
+@end example
+
+@noindent
+adds @code{my-text-hook-function} to the hook called @code{text-mode-hook}.
+
+If @var{function} is already present in @var{hook} (comparing using
+@code{equal}), then @code{add-hook} does not add it a second time.
+
+It is best to design your hook functions so that the order in which they
+are executed does not matter. Any dependence on the order is ``asking
+for trouble''. However, the order is predictable: normally,
+@var{function} goes at the front of the hook list, so it will be
+executed first (barring another @code{add-hook} call). If the optional
+argument @var{append} is non-@code{nil}, the new hook function goes at
+the end of the hook list and will be executed last.
+
+@code{add-hook} can handle the cases where @var{hook} is void or its
+value is a single function; it sets or changes the value to a list of
+functions.
+
+If @var{local} is non-@code{nil}, that says to add @var{function} to
+the buffer-local hook list instead of to the global hook list. If
+needed, this makes the hook buffer-local and adds @code{t} to the
+buffer-local value. The latter acts as a flag to run the hook
+functions in the default value as well as in the local value.
+@end defun
+
+@defun remove-hook hook function &optional local
+This function removes @var{function} from the hook variable
+@var{hook}. It compares @var{function} with elements of @var{hook}
+using @code{equal}, so it works for both symbols and lambda
+expressions.
+
+If @var{local} is non-@code{nil}, that says to remove @var{function}
+from the buffer-local hook list instead of from the global hook list.
+@end defun
+
@node Major Modes
@section Major Modes
@cindex major mode
-@cindex Fundamental mode
Major modes specialize Emacs for editing particular kinds of text.
Each buffer has only one major mode at a time. For each major mode
buffer, such as a local keymap. The effect lasts until you switch
to another major mode in the same buffer.
+@menu
+* Major Mode Basics::
+* Major Mode Conventions:: Coding conventions for keymaps, etc.
+* Example Major Modes:: Text mode and Lisp modes.
+* Auto Major Mode:: How Emacs chooses the major mode automatically.
+* Mode Help:: Finding out how to use a mode.
+* Derived Modes:: Defining a new major mode based on another major
+ mode.
+* Generic Modes:: Defining a simple major mode that supports
+ comment syntax and Font Lock mode.
+* Mode Hooks:: Hooks run at the end of major mode functions.
+@end menu
+
+@node Major Mode Basics
+@subsection Major Mode Basics
+@cindex Fundamental mode
+
The least specialized major mode is called @dfn{Fundamental mode}.
This mode has no mode-specific definitions or variable settings, so each
Emacs command behaves in its default manner, and each option is in its
parent argument, since it automatically enforces the most important
coding conventions for you.
-@findex define-generic-mode
For a very simple programming language major mode that handles
-comments and fontification, you can use @code{define-generic-mode}
-in @file{generic.el}.
+comments and fontification, you can use @code{define-generic-mode}.
+@xref{Generic Modes}.
Rmail Edit mode offers an example of changing the major mode
temporarily for a buffer, so it can be edited in a different way (with
are written. Text mode is perhaps the simplest major mode aside from
Fundamental mode. Rmail mode is a complicated and specialized mode.
-@menu
-* Major Mode Conventions:: Coding conventions for keymaps, etc.
-* Example Major Modes:: Text mode and Lisp modes.
-* Auto Major Mode:: How Emacs chooses the major mode automatically.
-* Mode Help:: Finding out how to use a mode.
-* Derived Modes:: Defining a new major mode based on another major
- mode.
-* Mode Hooks:: Hooks run at the end of major mode functions.
-@end menu
-
@node Major Mode Conventions
@subsection Major Mode Conventions
in a variable named @code{@var{modename}-mode-abbrev-table}. If the
major mode command defines any abbrevs itself, it should pass @code{t}
for the @var{system-flag} argument to @code{define-abbrev}.
-@xref{Abbrev Tables}.
+@xref{Defining Abbrevs}.
@item
The mode should specify how to do highlighting for Font Lock mode, by
@item
The mode should specify how Imenu should find the definitions or
sections of a buffer, by setting up a buffer-local value for the
-variable @code{imenu-generic-expression}, for the pair of variables
+variable @code{imenu-generic-expression}, for the two variables
@code{imenu-prev-index-position-function} and
@code{imenu-extract-index-name-function}, or for the variable
@code{imenu-create-index-function} (@pxref{Imenu}).
+@item
+The mode can specify a local value for
+@code{eldoc-documentation-function} to tell ElDoc mode how to handle
+this mode.
+
@item
Use @code{defvar} or @code{defcustom} to set mode-related variables, so
that they are not reinitialized if they already have a value. (Such
command (called the @dfn{parent mode}) and then alter some of its
settings. A mode that does this is called a @dfn{derived mode}. The
recommended way to define one is to use @code{define-derived-mode},
-but this is not required. Such a mode should use
-@code{delay-mode-hooks} around its entire body (including the call to
-the parent mode command) @emph{except} for the final call to
-@code{run-mode-hooks}, which runs the derived mode's hook. (Using
+but this is not required. Such a mode should call the parent mode
+command inside a @code{delay-mode-hooks} form. (Using
@code{define-derived-mode} does this automatically.) @xref{Derived
Modes}, and @ref{Mode Hooks}.
@item
If you want to make the new mode the default for files with certain
recognizable names, add an element to @code{auto-mode-alist} to select
-the mode for those file names. If you define the mode command to
-autoload, you should add this element in the same file that calls
-@code{autoload}. Otherwise, it is sufficient to add the element in the
-file that contains the mode definition. @xref{Auto Major Mode}.
+the mode for those file names (@pxref{Auto Major Mode}). If you
+define the mode command to autoload, you should add this element in
+the same file that calls @code{autoload}. If you use an autoload
+cookie for the mode command, you can also use an autoload cookie for
+the form that adds the element (@pxref{autoload cookie}). If you do
+not autoload the mode command, it is sufficient to add the element in
+the file that contains the mode definition.
@item
In the comments that document the file, you should provide a sample
@deffn Command normal-mode &optional find-file
This function establishes the proper major mode and buffer-local variable
-bindings for the current buffer. First it calls @code{set-auto-mode},
-then it runs @code{hack-local-variables} to parse, and bind or
-evaluate as appropriate, the file's local variables.
+bindings for the current buffer. First it calls @code{set-auto-mode}
+(see below), then it runs @code{hack-local-variables} to parse, and
+bind or evaluate as appropriate, the file's local variables
+(@pxref{File Local Variables}).
If the @var{find-file} argument to @code{normal-mode} is non-@code{nil},
@code{normal-mode} assumes that the @code{find-file} function is calling
-it. In this case, it may process a local variables list at the end of
-the file and in the @samp{-*-} line. The variable
+it. In this case, it may process local variables in the @samp{-*-}
+line or at the end of the file. The variable
@code{enable-local-variables} controls whether to do so. @xref{File
-variables, , Local Variables in Files, emacs, The GNU Emacs Manual}, for
-the syntax of the local variables section of a file.
+Variables, , Local Variables in Files, emacs, The GNU Emacs Manual},
+for the syntax of the local variables section of a file.
If you run @code{normal-mode} interactively, the argument
@var{find-file} is normally @code{nil}. In this case,
-@code{normal-mode} unconditionally processes any local variables list.
+@code{normal-mode} unconditionally processes any file local variables.
+
+If @code{normal-mode} processes the local variables list and this list
+specifies a major mode, that mode overrides any mode chosen by
+@code{set-auto-mode}. If neither @code{set-auto-mode} nor
+@code{hack-local-variables} specify a major mode, the buffer stays in
+the major mode determined by @code{default-major-mode} (see below).
@cindex file mode specification error
@code{normal-mode} uses @code{condition-case} around the call to the
mode specification error}, followed by the original error message.
@end deffn
-@defun set-auto-mode
+@defun set-auto-mode &optional keep-mode-if-same
@cindex visited file mode
This function selects the major mode that is appropriate for the
-current buffer. It may base its decision on the value of the @w{@samp{-*-}}
-line, on the visited file name (using @code{auto-mode-alist}), on the
-@w{@samp{#!}} line (using @code{interpreter-mode-alist}), or on the
-file's local variables list. However, this function does not look for
-the @samp{mode:} local variable near the end of a file; the
-@code{hack-local-variables} function does that. @xref{Choosing Modes, ,
-How Major Modes are Chosen, emacs, The GNU Emacs Manual}.
+current buffer. It bases its decision (in order of precedence) on
+the @w{@samp{-*-}} line, on the @w{@samp{#!}} line (using
+@code{interpreter-mode-alist}), on the text at the beginning of the
+buffer (using @code{magic-mode-alist}), and finally on the visited
+file name (using @code{auto-mode-alist}). @xref{Choosing Modes, , How
+Major Modes are Chosen, emacs, The GNU Emacs Manual}. However, this
+function does not look for the @samp{mode:} local variable near the
+end of a file; the @code{hack-local-variables} function does that.
+If @code{enable-local-variables} is @code{nil}, @code{set-auto-mode}
+does not check the @w{@samp{-*-}} line for a mode tag either.
+
+If @var{keep-mode-if-same} is non-@code{nil}, this function does not
+call the mode command if the buffer is already in the proper major
+mode. For instance, @code{set-visited-file-name} sets this to
+@code{t} to avoid killing buffer local variables that the user may
+have set.
@end defun
@defopt default-major-mode
standard value is @code{fundamental-mode}.
If the value of @code{default-major-mode} is @code{nil}, Emacs uses
-the (previously) current buffer's major mode for the major mode of a new
-buffer. However, if that major mode symbol has a @code{mode-class}
+the (previously) current buffer's major mode as the default major mode
+of a new buffer. However, if that major mode symbol has a @code{mode-class}
property with value @code{special}, then it is not used for new buffers;
Fundamental mode is used instead. The modes that have this property are
those such as Dired and Rmail that are useful only with text that has
@defun set-buffer-major-mode buffer
This function sets the major mode of @var{buffer} to the value of
-@code{default-major-mode}. If that variable is @code{nil}, it uses
-the current buffer's major mode (if that is suitable).
+@code{default-major-mode}; if that variable is @code{nil}, it uses the
+current buffer's major mode (if that is suitable). As an exception,
+if @var{buffer}'s name is @samp{*scratch*}, it sets the mode to
+@code{initial-major-mode}.
The low-level primitives for creating buffers do not use this function,
but medium-level commands such as @code{switch-to-buffer} and
@code{find-file-noselect} use it whenever they create buffers.
@end defun
-@defvar initial-major-mode
+@defopt initial-major-mode
@cindex @samp{*scratch*}
The value of this variable determines the major mode of the initial
@samp{*scratch*} buffer. The value should be a symbol that is a major
mode command. The default value is @code{lisp-interaction-mode}.
+@end defopt
+
+@defvar interpreter-mode-alist
+This variable specifies major modes to use for scripts that specify a
+command interpreter in a @samp{#!} line. Its value is an alist with
+elements of the form @code{(@var{interpreter} . @var{mode})}; for
+example, @code{("perl" . perl-mode)} is one element present by
+default. The element says to use mode @var{mode} if the file
+specifies an interpreter which matches @var{interpreter}.
+@end defvar
+
+@defvar magic-mode-alist
+This variable's value is an alist with elements of the form
+@code{(@var{regexp} . @var{function})}, where @var{regexp} is a
+regular expression and @var{function} is a function or @code{nil}.
+After visiting a file, @code{set-auto-mode} calls @var{function} if
+the text at the beginning of the buffer matches @var{regexp} and
+@var{function} is non-@code{nil}; if @var{function} is @code{nil},
+@code{auto-mode-alist} gets to decide the mode.
@end defvar
@defvar auto-mode-alist
This variable contains an association list of file name patterns
-(regular expressions; @pxref{Regular Expressions}) and corresponding
-major mode commands. Usually, the file name patterns test for suffixes,
-such as @samp{.el} and @samp{.c}, but this need not be the case. An
-ordinary element of the alist looks like @code{(@var{regexp} .
-@var{mode-function})}.
+(regular expressions) and corresponding major mode commands. Usually,
+the file name patterns test for suffixes, such as @samp{.el} and
+@samp{.c}, but this need not be the case. An ordinary element of the
+alist looks like @code{(@var{regexp} . @var{mode-function})}.
For example,
@end smallexample
When you visit a file whose expanded file name (@pxref{File Name
-Expansion}) matches a @var{regexp}, @code{set-auto-mode} calls the
-corresponding @var{mode-function}. This feature enables Emacs to select
-the proper major mode for most files.
+Expansion}), with version numbers and backup suffixes removed using
+@code{file-name-sans-versions} (@pxref{File Name Components}), matches
+a @var{regexp}, @code{set-auto-mode} calls the corresponding
+@var{mode-function}. This feature enables Emacs to select the proper
+major mode for most files.
If an element of @code{auto-mode-alist} has the form @code{(@var{regexp}
@var{function} t)}, then after calling @var{function}, Emacs searches
@end smallexample
@end defvar
-@defvar interpreter-mode-alist
-This variable specifies major modes to use for scripts that specify a
-command interpreter in a @samp{#!} line. Its value is a list of
-elements of the form @code{(@var{interpreter} . @var{mode})}; for
-example, @code{("perl" . perl-mode)} is one element present by default.
-The element says to use mode @var{mode} if the file specifies
-an interpreter which matches @var{interpreter}. The value of
-@var{interpreter} is actually a regular expression.
-
-This variable is applicable only when the @code{auto-mode-alist} does
-not indicate which major mode to use.
-@end defvar
-
@node Mode Help
@subsection Getting Help about a Major Mode
@cindex mode help
@end deffn
@defvar major-mode
-This variable holds the symbol for the current buffer's major mode.
-This symbol should have a function definition that is the command to
-switch to that major mode. The @code{describe-mode} function uses the
-documentation string of the function as the documentation of the major
-mode.
+This buffer-local variable holds the symbol for the current buffer's
+major mode. This symbol should have a function definition that is the
+command to switch to that major mode. The @code{describe-mode}
+function uses the documentation string of the function as the
+documentation of the major mode.
@end defvar
@node Derived Modes
@subsection Defining Derived Modes
+@cindex derived mode
It's often useful to define a new major mode in terms of an existing
one. An easy way to do this is to use @code{define-derived-mode}.
-@defmac define-derived-mode variant parent name docstring body@dots{}
+@defmac define-derived-mode variant parent name docstring keyword-args@dots{} body@dots{}
This construct defines @var{variant} as a major mode command, using
-@var{name} as the string form of the mode name.
+@var{name} as the string form of the mode name. @var{variant} and
+@var{parent} should be unquoted symbols.
The new command @var{variant} is defined to call the function
@var{parent}, then override certain aspects of that parent mode:
@itemize @bullet
@item
-The new mode has its own keymap, named @code{@var{variant}-map}.
-@code{define-derived-mode} initializes this map to inherit from
-@code{@var{parent}-map}, if it is not already set.
+The new mode has its own sparse keymap, named
+@code{@var{variant}-map}. @code{define-derived-mode}
+makes the parent mode's keymap the parent of the new map, unless
+@code{@var{variant}-map} is already set and already has a parent.
@item
The new mode has its own syntax table, kept in the variable
-@code{@var{variant}-syntax-table}.
-@code{define-derived-mode} initializes this variable by copying
-@code{@var{parent}-syntax-table}, if it is not already set.
+@code{@var{variant}-syntax-table}, unless you override this using the
+@code{:syntax-table} keyword (see below). @code{define-derived-mode}
+makes the parent mode's syntax-table the parent of
+@code{@var{variant}-syntax-table}, unless the latter is already set
+and already has a parent different from the standard syntax table.
@item
The new mode has its own abbrev table, kept in the variable
-@code{@var{variant}-abbrev-table}.
-@code{define-derived-mode} initializes this variable by copying
-@code{@var{parent}-abbrev-table}, if it is not already set.
+@code{@var{variant}-abbrev-table}, unless you override this using the
+@code{:abbrev-table} keyword (see below).
@item
-The new mode has its own mode hook, @code{@var{variant}-hook},
-which it runs in standard fashion as the very last thing that it does.
-(The new mode also runs the mode hook of @var{parent} as part
-of calling @var{parent}.)
+The new mode has its own mode hook, @code{@var{variant}-hook}. It
+runs this hook, after running the hooks of its ancestor modes, with
+@code{run-mode-hooks}, as the last thing it does. @xref{Mode Hooks}.
@end itemize
In addition, you can specify how to override other aspects of
@var{parent} with @var{body}. The command @var{variant}
evaluates the forms in @var{body} after setting up all its usual
-overrides, just before running @code{@var{variant}-hook}.
+overrides, just before running the mode hooks.
+
+You can also specify @code{nil} for @var{parent}. This gives the new
+mode no parent. Then @code{define-derived-mode} behaves as described
+above, but, of course, omits all actions connected with @var{parent}.
+
+The argument @var{docstring} specifies the documentation string for
+the new mode. @code{define-derived-mode} adds some general
+information about the mode's hook, followed by the mode's keymap, at
+the end of this docstring. If you omit @var{docstring},
+@code{define-derived-mode} generates a documentation string.
+
+The @var{keyword-args} are pairs of keywords and values. The values
+are evaluated. The following keywords are currently supported:
-The argument @var{docstring} specifies the documentation string for the
-new mode. If you omit @var{docstring}, @code{define-derived-mode}
-generates a documentation string.
+@table @code
+@item :syntax-table
+You can use this to explicitly specify a syntax table for the new
+mode. If you specify a @code{nil} value, the new mode uses the same
+syntax table as @var{parent}, or the standard syntax table if
+@var{parent} is @code{nil}. (Note that this does @emph{not} follow
+the convention used for non-keyword arguments that a @code{nil} value
+is equivalent with not specifying the argument.)
+
+@item :abbrev-table
+You can use this to explicitly specify an abbrev table for the new
+mode. If you specify a @code{nil} value, the new mode uses the same
+abbrev table as @var{parent}, or @code{fundamental-mode-abbrev-table}
+if @var{parent} is @code{nil}. (Again, a @code{nil} value is
+@emph{not} equivalent to not specifying this keyword.)
+
+@item :group
+If this is specified, the value should be the customization group for
+this mode. (Not all major modes have one.) Only the (still
+experimental and unadvertised) command @code{customize-mode} currently
+uses this. @code{define-derived-mode} does @emph{not} automatically
+define the specified customization group.
+@end table
Here is a hypothetical example:
@code{define-derived-mode} does that automatically.
@end defmac
+@node Generic Modes
+@subsection Generic Modes
+@cindex generic mode
+
+@dfn{Generic modes} are simple major modes with basic support for
+comment syntax and Font Lock mode. They are primarily useful for
+configuration files. To define a generic mode, use the macro
+@code{define-generic-mode}. See the file @file{generic-x.el} for some
+examples of the use of @code{define-generic-mode}.
+
+@defmac define-generic-mode mode comment-list keyword-list font-lock-list auto-mode-list function-list &optional docstring
+This macro creates a new generic mode. The argument @var{mode} (an
+unquoted symbol) is the major mode command. The optional argument
+@var{docstring} is the documentation for the mode command. If you do
+not supply it, @code{define-generic-mode} uses a default documentation
+string instead.
+
+@var{comment-list} is a list in which each element is either a
+character, a string of one or two characters, or a cons cell. A
+character or a string is set up in the mode's syntax table as a
+``comment starter.'' If the entry is a cons cell, the @sc{car} is set
+up as a ``comment starter'' and the @sc{cdr} as a ``comment ender.''
+(Use @code{nil} for the latter if you want comments to end at the end
+of the line.) Note that the syntax table has limitations about what
+comment starters and enders are actually possible. @xref{Syntax
+Tables}.
+
+@var{keyword-list} is a list of keywords to highlight with
+@code{font-lock-keyword-face}. Each keyword should be a string.
+@var{font-lock-list} is a list of additional expressions to highlight.
+Each element of this list should have the same form as an element of
+@code{font-lock-keywords}. @xref{Search-based Fontification}.
+
+@var{auto-mode-list} is a list of regular expressions to add to the
+variable @code{auto-mode-alist}. These regular expressions are added
+when Emacs runs the macro expansion.
+
+@var{function-list} is a list of functions to call to do some
+additional setup. The mode command calls these functions just before
+it runs the mode hook variable @code{@var{mode}-hook}.
+@end defmac
+
@node Mode Hooks
@subsection Mode Hooks
-The two last things a major mode function does is to run its mode
+ The two last things a major mode function should do is run its mode
hook and finally the mode independent normal hook
@code{after-change-major-mode-hook}. If the major mode is a derived
mode, that is if it calls another major mode (the parent mode) in its
mode's hook. Neither the parent's mode hook nor
@code{after-change-major-mode-hook} are run at the end of the actual
call to the parent mode. This applies recursively if the parent mode
-has itself a parent. That is, the mode hooks of all major modes called
-directly or indirectly by the major mode function are all run in
-sequence at the end, just before @code{after-change-major-mode-hook}.
-
-If you are customizing a major mode, rather than defining one, the
-above is all you need to know about the hooks run at the end of a
-major mode. This also applies if you use @code{define-derived-mode}
-to define a major mode, because that macro will automatically
-implement the above for you.
-
-Programmers wishing to define a major mode without using
-@code{define-derived-mode}, should make sure that their major mode
-follows the above conventions. @xref{Major Mode Conventions}, for how
-this should be accomplished. Below, we give some implementation
-details.
+has itself a parent. That is, the mode hooks of all major modes
+called directly or indirectly by the major mode function are all run
+in sequence at the end, just before
+@code{after-change-major-mode-hook}.
+
+ These conventions are new in Emacs 22, and some major modes
+implemented by users do not follow them yet. So if you put a function
+onto @code{after-change-major-mode-hook}, keep in mind that some modes
+will fail to run it. If a user complains about that, you can respond,
+``That major mode fails to follow Emacs conventions, and that's why it
+fails to work. Please fix the major mode.'' In most cases, that is
+good enough, so go ahead and use @code{after-change-major-mode-hook}.
+However, if a certain feature needs to be completely reliable,
+it should not use @code{after-change-major-mode-hook} as of yet.
+
+ When you defined a major mode using @code{define-derived-mode}, it
+automatically makes sure these conventions are followed. If you
+define a major mode ``from scratch'', not using
+@code{define-derived-mode}, make sure the major mode command follows
+these and other conventions. @xref{Major Mode Conventions}. You use
+these functions to do it properly.
@defun run-mode-hooks &rest hookvars
Major modes should run their mode hook using this function. It is
-similar to @code{run-hooks} (@pxref{Hooks}), but if run inside a
-@code{delay-mode-hooks} form, this function does not run any hooks.
-Instead, it arranges for @var{hookvars} to be run at a later call to
-the function. Otherwise, @code{run-mode-hooks} runs any delayed hooks
-in order, then @var{hookvars} and finally
+similar to @code{run-hooks} (@pxref{Hooks}), but it also runs
@code{after-change-major-mode-hook}.
+
+When the call to this function is dynamically inside a
+@code{delay-mode-hooks} form, this function does not run any hooks.
+Instead, it arranges for the next call to @code{run-mode-hooks} to run
+@var{hookvars}.
@end defun
-@defmac delay-mode-hooks body...
+@defmac delay-mode-hooks body@dots{}
This macro executes @var{body} like @code{progn}, but all calls to
@code{run-mode-hooks} inside @var{body} delay running their hooks.
They will be run by the first call to @code{run-mode-hooks} after exit
-from @code{delay-mode-hooks}.
+from @code{delay-mode-hooks}. This is the proper way for a major mode
+command to invoke its parent mode.
@end defmac
@defvar after-change-major-mode-hook
Every major mode function should run this normal hook at its very end.
It normally does not need to do so explicitly. Indeed, a major mode
function should normally run its mode hook with @code{run-mode-hooks}
-as the very last thing it does and @code{run-mode-hooks} runs
-@code{after-change-major-mode-hook} at its very end.
+as the very last thing it does, and the last thing
+@code{run-mode-hooks} does is run @code{after-change-major-mode-hook}.
@end defvar
@node Minor Modes
There are conventions for writing minor modes just as there are for
major modes. Several of the major mode conventions apply to minor
modes as well: those regarding the name of the mode initialization
-function, the names of global symbols, and the use of keymaps and
-other tables.
+function, the names of global symbols, the use of a hook at the end of
+the initialization function, and the use of keymaps and other tables.
In addition, there are several conventions that are specific to
minor modes. (The easiest way to follow all the conventions is to use
@item
Add an element to @code{minor-mode-alist} for each minor mode
-(@pxref{Mode Line Variables}), if you want to indicate the minor mode in
-the mode line. This element should be a list of the following form:
+(@pxref{Definition of minor-mode-alist}), if you want to indicate the
+minor mode in the mode line. This element should be a list of the
+following form:
@smallexample
(@var{mode-variable} @var{string})
invoking the mode command. Note in the variable's documentation string that
setting the variable other than via Custom may not take effect.
- Also mark the definition with an autoload cookie (@pxref{Autoload}),
+ Also mark the definition with an autoload cookie (@pxref{autoload cookie}),
and specify a @code{:require} so that customizing the variable will load
the library that defines the mode. This will copy suitable definitions
into @file{loaddefs.el} so that users can use @code{customize-option} to
"Toggle msb-mode.
Setting this variable directly does not take effect;
use either \\[customize] or the function `msb-mode'."
- :set (lambda (symbol value)
- (msb-mode (or value 0)))
+ :set 'custom-set-minor-mode
:initialize 'custom-initialize-default
:version "20.4"
:type 'boolean
Each minor mode can have its own keymap, which is active when the mode
is enabled. To set up a keymap for a minor mode, add an element to the
-alist @code{minor-mode-map-alist}. @xref{Active Keymaps}.
+alist @code{minor-mode-map-alist}. @xref{Definition of minor-mode-map-alist}.
@cindex @code{self-insert-command}, minor modes
One use of minor mode keymaps is to modify the behavior of certain
The macro @code{define-minor-mode} offers a convenient way of
implementing a mode in one self-contained definition.
-@defmac define-minor-mode mode doc [init-value [lighter [keymap]]] keyword-args... body...
+@defmac define-minor-mode mode doc [init-value [lighter [keymap]]] keyword-args@dots{} body@dots{}
@tindex define-minor-mode
This macro defines a new minor mode whose name is @var{mode} (a
symbol). It defines a command named @var{mode} to toggle the minor
mode, with @var{doc} as its documentation string. It also defines a
variable named @var{mode}, which is set to @code{t} or @code{nil} by
enabling or disabling the mode. The variable is initialized to
-@var{init-value}.
+@var{init-value}. Except in unusual circumstances (see below), this
+value must be @code{nil}.
The string @var{lighter} says what to display in the mode line
when the mode is enabled; if it is @code{nil}, the mode is not displayed
@table @code
@item :group @var{group}
Custom group name to use in all generated @code{defcustom} forms.
-Defaults to @var{mode} without the possible trailing @samp{-mode}. Be
-aware that this default may not be a valid customization group defined
-with @code{defgroup}. Please make sure it is.
+Defaults to @var{mode} without the possible trailing @samp{-mode}.
+@strong{Warning:} don't use this default group name unless you have
+written a @code{defgroup} to define that group properly. @xref{Group
+Definitions}.
@item :global @var{global}
-If non-@code{nil} specifies that the minor mode should be global.
-By default, minor modes are buffer-local.
+If non-@code{nil} specifies that the minor mode should be global. By
+default, minor modes defined with @code{define-minor-mode} are
+buffer-local.
@item :init-value @var{init-value}
This is equivalent to specifying @var{init-value} positionally.
This is equivalent to specifying @var{keymap} positionally.
@end table
-Any other keyword arguments are passed passed directly to the
+Any other keyword arguments are passed directly to the
@code{defcustom} generated for the variable @var{mode}.
-The command named @var{mode} finishes by executing the @var{body} forms,
-if any, after it has performed the standard actions such as setting
-the variable named @var{mode}.
+The command named @var{mode} first performs the standard actions such
+as setting the variable named @var{mode} and then executes the
+@var{body} forms, if any. It finishes by running the mode hook
+variable @code{@var{mode}-hook}.
@end defmac
+ The initial value must be @code{nil} except in cases where (1) the
+mode is preloaded in Emacs, or (2) it is painless for loading to
+enable the mode even though the user did not request it. For
+instance, if the mode has no effect unless something else is enabled,
+and will always be loaded by that time, enabling it by default is
+harmless. But these are unusual circumstances. Normally, the
+initial value must be @code{nil}.
+
@findex easy-mmode-define-minor-mode
The name @code{easy-mmode-define-minor-mode} is an alias
for this macro.
gobbles all preceding whitespace except the last.
See the command \\[hungry-electric-delete]."
;; The initial value.
- :initial-value nil
+ :init-value nil
;; The indicator for the mode line.
:lighter " Hungry"
;; The minor mode bindings.
:group 'hunger)
@end smallexample
+@defmac define-global-minor-mode global-mode mode turn-on keyword-args@dots{}
+This defines a global minor mode named @var{global-mode} whose meaning
+is to enable the buffer-local minor mode @var{mode} in every buffer.
+To turn on the minor mode in a buffer, it uses the function
+@var{turn-on}; to turn off the minor mode, it calls @code{mode} with
+@minus{}1 as argument.
+
+Use @code{:group @var{group}} in @var{keyword-args} to specify the
+custom group for the mode variable of the global minor mode.
+@end defmac
+
@node Mode Line Format
@section Mode-Line Format
@cindex mode line
information displayed in the mode line relates to the enabled major and
minor modes.
+@menu
+* Base: Mode Line Basics. Basic ideas of mode line control.
+* Data: Mode Line Data. The data structure that controls the mode line.
+* Top: Mode Line Top. The top level variable, mode-line-format.
+* Mode Line Variables:: Variables used in that data structure.
+* %-Constructs:: Putting information into a mode line.
+* Properties in Mode:: Using text properties in the mode line.
+* Header Lines:: Like a mode line, but at the top.
+* Emulating Mode Line:: Formatting text as the mode line would.
+@end menu
+
+@node Mode Line Basics
+@subsection Mode Line Basics
+
@code{mode-line-format} is a buffer-local variable that holds a
-template used to display the mode line of the current buffer. All
-windows for the same buffer use the same @code{mode-line-format}, so
-their mode lines appear the same---except for scrolling percentages, and
-line and column numbers, since those depend on point and on how the
-window is scrolled. @code{header-line-format} is used likewise for
-header lines.
+@dfn{mode line construct}, a kind of template, which controls the
+display the mode line of the current buffer. All windows for the same
+buffer use the same @code{mode-line-format}, so their mode lines
+appear the same---except for scrolling percentages, and line and
+column numbers, since those depend on point and on how the window is
+scrolled. The value of @code{header-line-format} specifies the
+buffer's header line in the same way, with a mode line construct.
For efficiency, Emacs does not recompute the mode line and header
line of a window in every redisplay. It does so when circumstances
color using the face @code{mode-line}. Other windows' mode lines
appear in the face @code{mode-line-inactive} instead. @xref{Faces}.
- A window that is just one line tall does not display either a mode
-line or a header line, even if the variables call for one. A window
-that is two lines tall cannot display both a mode line and a header
-line at once; if the variables call for both, only the mode line
-actually appears.
-
-@menu
-* Mode Line Data:: The data structure that controls the mode line.
-* Mode Line Variables:: Variables used in that data structure.
-* %-Constructs:: Putting information into a mode line.
-* Properties in Mode:: Using text properties in the mode line.
-* Header Lines:: Like a mode line, but at the top.
-* Emulating Mode Line:: Formatting text as the mode line would.
-@end menu
-
@node Mode Line Data
@subsection The Data Structure of the Mode Line
@cindex mode-line construct
- The mode-line contents are controlled by a data structure of lists,
-strings, symbols, and numbers kept in buffer-local variables. The data
-structure is called a @dfn{mode-line construct}, and it is built in
-recursive fashion out of simpler mode-line constructs. The same data
-structure is used for constructing frame titles (@pxref{Frame Titles})
-and header lines (@pxref{Header Lines}).
-
-@defvar mode-line-format
-The value of this variable is a mode-line construct with overall
-responsibility for the mode-line format. The value of this variable
-controls which other variables are used to form the mode-line text, and
-where they appear.
+ The mode-line contents are controlled by a data structure called a
+@dfn{mode-line construct}, made up of lists, strings, symbols, and
+numbers kept in buffer-local variables. Each data type has a specific
+meaning for the mode-line appearance, as described below. The same
+data structure is used for constructing frame titles (@pxref{Frame
+Titles}) and header lines (@pxref{Header Lines}).
-If you set this variable to @code{nil} in a buffer, that buffer does not
-have a mode line.
-@end defvar
+ A mode-line construct may be as simple as a fixed string of text,
+but it usually specifies how to combine fixed strings with variables'
+values to construct the text. Many of these variables are themselves
+defined to have mode-line constructs as their values.
- A mode-line construct may be as simple as a fixed string of text, but
-it usually specifies how to use other variables to construct the text.
-Many of these variables are themselves defined to have mode-line
-constructs as their values.
-
- The default value of @code{mode-line-format} incorporates the values
-of variables such as @code{mode-line-position} and
-@code{mode-line-modes} (which in turn incorporates the values of the
-variables @code{mode-name} and @code{minor-mode-alist}). Because of
-this, very few modes need to alter @code{mode-line-format} itself. For
-most purposes, it is sufficient to alter some of the variables that
-@code{mode-line-format} either directly or indirectly refers to.
-
- A mode-line construct may be a list, a symbol, or a string. If the
-value is a list, each element may be a list, a symbol, or a string.
-
- The mode line can display various faces, if the strings that control
-it have the @code{face} property. @xref{Properties in Mode}. In
-addition, the face @code{mode-line} is used as a default for the whole
-mode line (@pxref{Standard Faces}).
+ Here are the meanings of various data types as mode-line constructs:
@table @code
@cindex percent symbol in mode line
@item @var{string}
-A string as a mode-line construct is displayed verbatim in the mode line
-except for @dfn{@code{%}-constructs}. Decimal digits after the @samp{%}
-specify the field width for space filling on the right (i.e., the data
-is left justified). @xref{%-Constructs}.
+A string as a mode-line construct appears verbatim in the mode line
+except for @dfn{@code{%}-constructs} in it. These stand for
+substitution of other data; see @ref{%-Constructs}.
+
+If the string has @code{face} properties, they are copied into the
+mode line contents too (@pxref{Properties in Mode}). Any characters
+in the mode line which have no @code{face} properties are displayed,
+by default, in the face @code{mode-line} or @code{mode-line-inactive}
+(@pxref{Standard Faces,,, emacs, The GNU Emacs Manual}).
@item @var{symbol}
A symbol as a mode-line construct stands for its value. The value of
displayed verbatim: the @code{%}-constructs are not recognized.
Unless @var{symbol} is marked as ``risky'' (i.e., it has a
-non-@code{nil} @code{risky-local-variable} property), all properties in
-any strings, as well as all @code{:eval} and @code{:propertize} forms in
-the value of that symbol will be ignored.
+non-@code{nil} @code{risky-local-variable} property), all text
+properties specified in @var{symbol}'s value are ignored. This
+includes the text properties of strings in @var{symbol}'s value, as
+well as all @code{:eval} and @code{:propertize} forms in it.
-@item (@var{string} @var{rest}@dots{}) @r{or} (@var{list} @var{rest}@dots{})
+@item (@var{string} @var{rest}@dots{})
+@itemx (@var{list} @var{rest}@dots{})
A list whose first element is a string or list means to process all the
elements recursively and concatenate the results. This is the most
common form of mode-line construct.
@item (:eval @var{form})
A list whose first element is the symbol @code{:eval} says to evaluate
-@var{form}, and use the result as a string to display.
+@var{form}, and use the result as a string to display. Make sure this
+evaluation cannot load any files, as doing so could cause infinite
+recursion.
@item (:propertize @var{elt} @var{props}@dots{})
A list whose first element is the symbol @code{:propertize} says to
-process the mode-line construct @var{elt} recursively and add the text
+process the mode-line construct @var{elt} recursively, then add the text
properties specified by @var{props} to the result. The argument
@var{props} should consist of zero or more pairs @var{text-property}
@var{value}. (This feature is new as of Emacs 22.1.)
@item (@var{symbol} @var{then} @var{else})
-A list whose first element is a symbol that is not a keyword specifies a
-conditional. Its meaning depends on the value of @var{symbol}. If the
-value is non-@code{nil}, the second element, @var{then}, is processed
-recursively as a mode-line element. But if the value of @var{symbol} is
-@code{nil}, the third element, @var{else}, is processed recursively.
-You may omit @var{else}; then the mode-line element displays nothing if
-the value of @var{symbol} is @code{nil}.
+A list whose first element is a symbol that is not a keyword specifies
+a conditional. Its meaning depends on the value of @var{symbol}. If
+@var{symbol} has a non-@code{nil} value, the second element,
+@var{then}, is processed recursively as a mode-line element.
+Otherwise, the third element, @var{else}, is processed recursively.
+You may omit @var{else}; then the mode-line element displays nothing
+if the value of @var{symbol} is @code{nil} or void.
@item (@var{width} @var{rest}@dots{})
A list whose first element is an integer specifies truncation or
padding of the results of @var{rest}. The remaining elements
@var{rest} are processed recursively as mode-line constructs and
-concatenated together. Then the result is space filled (if
-@var{width} is positive) or truncated (to @minus{}@var{width} columns,
-if @var{width} is negative) on the right.
+concatenated together. When @var{width} is positive, the result is
+space filled on the right if its width is less than @var{width}. When
+@var{width} is negative, the result is truncated on the right to
+@minus{}@var{width} columns if its width exceeds @minus{}@var{width}.
For example, the usual way to show what percentage of a buffer is above
the top of the window is to use a list like this: @code{(-3 "%p")}.
@end table
+@node Mode Line Top
+@subsection The Top Level of Mode Line Control
+
+ The variable in overall control of the mode line is
+@code{mode-line-format}.
+
+@defvar mode-line-format
+The value of this variable is a mode-line construct that controls the
+contents of the mode-line. It is always buffer-local in all buffers.
+
+If you set this variable to @code{nil} in a buffer, that buffer does
+not have a mode line. (A window that is just one line tall never
+displays a mode line.)
+@end defvar
+
+ The default value of @code{mode-line-format} is designed to use the
+values of other variables such as @code{mode-line-position} and
+@code{mode-line-modes} (which in turn incorporates the values of the
+variables @code{mode-name} and @code{minor-mode-alist}). Very few
+modes need to alter @code{mode-line-format} itself. For most
+purposes, it is sufficient to alter some of the variables that
+@code{mode-line-format} either directly or indirectly refers to.
+
If you do alter @code{mode-line-format} itself, the new value should
use the same variables that appear in the default value (@pxref{Mode
Line Variables}), rather than duplicating their contents or displaying
@node Mode Line Variables
@subsection Variables Used in the Mode Line
- This section describes variables incorporated by the
-standard value of @code{mode-line-format} into the text of the mode
-line. There is nothing inherently special about these variables; any
-other variables could have the same effects on the mode line if
-@code{mode-line-format} were changed to use them.
+ This section describes variables incorporated by the standard value
+of @code{mode-line-format} into the text of the mode line. There is
+nothing inherently special about these variables; any other variables
+could have the same effects on the mode line if
+@code{mode-line-format}'s value were changed to use them. However,
+various parts of Emacs set these variables on the understanding that
+they will control parts of the mode line; therefore, practically
+speaking, it is essential for the mode line to use them.
@defvar mode-line-mule-info
This variable holds the value of the mode-line construct that displays
@end defvar
@defvar minor-mode-alist
+@anchor{Definition of minor-mode-alist}
This variable holds an association list whose elements specify how the
mode line should indicate that a minor mode is active. Each element of
the @code{minor-mode-alist} should be a two-element list:
@node %-Constructs
@subsection @code{%}-Constructs in the Mode Line
- The following table lists the recognized @code{%}-constructs and what
-they mean. In any construct except @samp{%%}, you can add a decimal
-integer after the @samp{%} to specify how many characters to display.
+ Strings used as mode-line constructs can use certain
+@code{%}-constructs to substitute various kinds of data. Here is a
+list of the defined @code{%}-constructs, and what they mean. In any
+construct except @samp{%%}, you can add a decimal integer after the
+@samp{%} to specify a minimum field width. If the width is less, the
+field is padded with spaces to the right.
@table @code
@item %b
@item %F
The title (only on a window system) or the name of the selected frame.
-@xref{Window Frame Parameters}.
+@xref{Basic Parameters}.
@item %i
The size of the accessible part of the current buffer; basically
The value of @code{mode-name}.
@item %M
-The value of @code{global-mode-string}. Currently, only
-@code{display-time} modifies the value of @code{global-mode-string}.
+The value of @code{global-mode-string}.
@end table
@node Properties in Mode
Certain text properties are meaningful in the
mode line. The @code{face} property affects the appearance of text; the
-@code{help-echo} property associate help strings with the text, and
+@code{help-echo} property associates help strings with the text, and
@code{local-map} can make the text mouse-sensitive.
There are four ways to specify text properties for text in the mode
It is normally @code{nil}, so that ordinary buffers have no header line.
@end defvar
+ A window that is just one line tall never displays a header line. A
+window that is two lines tall cannot display both a mode line and a
+header line at once; if it has a mode line, then it does not display a
+header line.
+
@node Emulating Mode Line
@subsection Emulating Mode-Line Formatting
You can use the function @code{format-mode-line} to compute
the text that would appear in a mode line or header line
-based on certain mode-line specification.
+based on a certain mode-line specification.
@defun format-mode-line format &optional face window buffer
This function formats a line of text according to @var{format} as if
for which no @code{face} property is specified gets a default
value which is usually @var{face}. (If @var{face} is @code{t},
that stands for either @code{mode-line} if @var{window} is selected,
-otherwise @code{mode-line-inactive}.)
+otherwise @code{mode-line-inactive}. If @var{face} is @code{nil} or
+omitted, that stands for no face property.)
However, if @var{face} is an integer, the value has no text properties.
(@var{menu-title} @var{regexp} @var{index} @var{function} @var{arguments}@dots{})
@end example
-Like in the previous case, each match for this element creates an
-index item. However, if this index item is selected by the user, it
-calls @var{function} with arguments consisting of the item name, the
-buffer position, and @var{arguments}.
+Each match for this element creates an index item, and when the index
+item is selected by the user, it calls @var{function} with arguments
+consisting of the item name, the buffer position, and @var{arguments}.
For Emacs Lisp mode, @code{imenu-generic-expression} could look like
this:
finds the next ``definition'' to put in the buffer index, scanning
backward in the buffer from point. It should return @code{nil} if it
doesn't find another ``definition'' before point. Otherwise it should
-leave point at the place it finds a ``definition,'' and return any
+leave point at the place it finds a ``definition'' and return any
non-@code{nil} value.
Setting this variable makes it buffer-local in the current buffer.
It creates the submenu @var{menu-title} specified by @var{sub-alist}.
The default value of @code{imenu-create-index-function} is
-@code{imenu-default-create-index-function}. This function uses
-@code{imenu-prev-index-position-function} and
+@code{imenu-default-create-index-function}. This function calls the
+value of @code{imenu-prev-index-position-function} and the value of
@code{imenu-extract-index-name-function} to produce the index alist.
However, if either of these two variables is @code{nil}, the default
function uses @code{imenu-generic-expression} instead.
which contexts. This section explains how to customize Font Lock for a
particular major mode.
- Font Lock mode finds text to highlight in two ways: through syntactic
-parsing based on the syntax table, and through searching (usually for
-regular expressions). Syntactic fontification happens first; it finds
-comments and string constants, and highlights them using
-@code{font-lock-comment-face} and @code{font-lock-string-face}
-(@pxref{Faces for Font Lock}). Search-based fontification follows.
+ Font Lock mode finds text to highlight in two ways: through
+syntactic parsing based on the syntax table, and through searching
+(usually for regular expressions). Syntactic fontification happens
+first; it finds comments and string constants and highlights them.
+Search-based fontification happens second.
@menu
* Font Lock Basics:: Overview of customizing Font Lock.
* Search-based Fontification:: Fontification based on regexps.
+* Customizing Keywords:: Customizing search-based fontification.
* Other Font Lock Variables:: Additional customization facilities.
* Levels of Font Lock:: Each mode can define alternative levels
so that the user can select more or less.
* Precalculated Fontification:: How Lisp programs that produce the buffer
contents can also specify how to fontify it.
* Faces for Font Lock:: Special faces specifically for Font Lock.
-* Syntactic Font Lock:: Defining character syntax based on context
+* Syntactic Font Lock:: Fontification based on syntax tables.
+* Setting Syntax Properties:: Defining character syntax based on context
using the Font Lock mechanism.
+* Multiline Font Lock:: How to coerce Font Lock into properly
+ highlighting multiline constructs.
@end menu
@node Font Lock Basics
@defvar font-lock-defaults
This variable is set by major modes, as a buffer-local variable, to
-specify how to fontify text in that mode. The value should look like
-this:
+specify how to fontify text in that mode. It automatically becomes
+buffer-local when you set it. The value should look like this:
@example
-(@var{keywords} @var{keywords-only} @var{case-fold}
- @var{syntax-alist} @var{syntax-begin} @var{other-vars}@dots{})
+(@var{keywords} [@var{keywords-only} [@var{case-fold}
+ [@var{syntax-alist} [@var{syntax-begin} @var{other-vars}@dots{}]]]])
@end example
The first element, @var{keywords}, indirectly specifies the value of
-@code{font-lock-keywords}. It can be a symbol, a variable whose value
-is the list to use for @code{font-lock-keywords}. It can also be a list of
-several such symbols, one for each possible level of fontification. The
-first symbol specifies how to do level 1 fontification, the second
-symbol how to do level 2, and so on.
+@code{font-lock-keywords} which directs search-based fontification.
+It can be a symbol, a variable or a function whose value is the list
+to use for @code{font-lock-keywords}. It can also be a list of
+several such symbols, one for each possible level of fontification.
+The first symbol specifies how to do level 1 fontification, the second
+symbol how to do level 2, and so on. @xref{Levels of Font Lock}.
The second element, @var{keywords-only}, specifies the value of the
variable @code{font-lock-keywords-only}. If this is non-@code{nil},
syntactic fontification (of strings and comments) is not performed.
+@xref{Syntactic Font Lock}.
The third element, @var{case-fold}, specifies the value of
-@code{font-lock-keywords-case-fold-search}. If it is non-@code{nil}, Font Lock
-mode ignores case when searching as directed by
+@code{font-lock-keywords-case-fold-search}. If it is non-@code{nil},
+Font Lock mode ignores case when searching as directed by
@code{font-lock-keywords}.
-If the fourth element, @var{syntax-alist}, is non-@code{nil}, it should be
-a list of cons cells of the form @code{(@var{char-or-string}
+If the fourth element, @var{syntax-alist}, is non-@code{nil}, it
+should be a list of cons cells of the form @code{(@var{char-or-string}
. @var{string})}. These are used to set up a syntax table for
-fontification (@pxref{Syntax Table Functions}). The resulting syntax
-table is stored in @code{font-lock-syntax-table}.
+syntactic fontification (@pxref{Syntax Table Functions}). The
+resulting syntax table is stored in @code{font-lock-syntax-table}.
The fifth element, @var{syntax-begin}, specifies the value of
-@code{font-lock-beginning-of-syntax-function} (see below).
+@code{font-lock-beginning-of-syntax-function}. We recommend setting
+this variable to @code{nil} and using @code{syntax-begin-function}
+instead.
All the remaining elements (if any) are collectively called
@var{other-vars}. Each of these elements should have the form
-@code{(@var{variable} . @var{value})}---which means, make @var{variable}
-buffer-local and then set it to @var{value}. You can use these
-@var{other-vars} to set other variables that affect fontification,
-aside from those you can control with the first five elements.
+@code{(@var{variable} . @var{value})}---which means, make
+@var{variable} buffer-local and then set it to @var{value}. You can
+use these @var{other-vars} to set other variables that affect
+fontification, aside from those you can control with the first five
+elements. @xref{Other Font Lock Variables}.
@end defvar
@node Search-based Fontification
The most important variable for customizing Font Lock mode is
@code{font-lock-keywords}. It specifies the search criteria for
-search-based fontification.
+search-based fontification. You should specify the value of this
+variable with @var{keywords} in @code{font-lock-defaults}.
@defvar font-lock-keywords
This variable's value is a list of the keywords to highlight. Be
@end example
If you use @code{regexp-opt} to produce the regular expression
-@var{matcher}, then you can use @code{regexp-opt-depth} (@pxref{Regexp
+@var{matcher}, you can use @code{regexp-opt-depth} (@pxref{Regexp
Functions}) to calculate the value for @var{subexp}.
@item (@var{matcher} . @var{facespec})
@code{font-lock-extra-managed-props} so that the properties will also
be cleared out when they are no longer appropriate. Alternatively,
you can set the variable @code{font-lock-unfontify-region-function} to
-a function that clears these properties.
+a function that clears these properties. @xref{Other Font Lock
+Variables}.
@item (@var{matcher} . @var{subexp-highlighter})
In this kind of element, @var{subexp-highlighter} is a list
@end table
@strong{Warning:} Do not design an element of @code{font-lock-keywords}
-to match text which spans lines; this does not work reliably. While
-@code{font-lock-fontify-buffer} handles multi-line patterns correctly,
-updating when you edit the buffer does not, since it considers text one
-line at a time. If you have patterns that typically only span one
-line but can occasionally span two or three, such as
-@samp{<title>...</title>}, you can ask Font Lock to be more careful by
-setting @code{font-lock-multiline} to @code{t}. But it still will not
-work in all cases.
+to match text which spans lines; this does not work reliably.
+For details, see @xref{Multiline Font Lock}.
-@node Other Font Lock Variables
-@subsection Other Font Lock Variables
-
- This section describes additional variables that a major mode
-can set by means of @code{font-lock-defaults}.
-
-@defvar font-lock-keywords-only
-Non-@code{nil} means Font Lock should not fontify comments or strings
-syntactically; it should only fontify based on
-@code{font-lock-keywords}.
-@end defvar
-
-@ignore
-Other variables include those for buffer-specialized fontification functions,
-`font-lock-fontify-buffer-function', `font-lock-unfontify-buffer-function',
-`font-lock-fontify-region-function', `font-lock-unfontify-region-function',
-`font-lock-inhibit-thing-lock' and `font-lock-maximum-size'.
-@end ignore
+You can use @var{case-fold} in @code{font-lock-defaults} to specify
+the value of @code{font-lock-keywords-case-fold-search} which says
+whether search-based fontification should be case-insensitive.
@defvar font-lock-keywords-case-fold-search
Non-@code{nil} means that regular expression matching for the sake of
@code{font-lock-keywords} should be case-insensitive.
@end defvar
-@defvar font-lock-syntax-table
-This variable specifies the syntax table to use for fontification of
-comments and strings.
-@end defvar
+@node Customizing Keywords
+@subsection Customizing Search-Based Fontification
+
+ You can use @code{font-lock-add-keywords} to add additional
+search-based fontification rules to a major mode, and
+@code{font-lock-remove-keywords} to removes rules.
+
+@defun font-lock-add-keywords mode keywords &optional how
+This function adds highlighting @var{keywords}, for the current buffer
+or for major mode @var{mode}. The argument @var{keywords} should be a
+list with the same format as the variable @code{font-lock-keywords}.
+
+If @var{mode} is a symbol which is a major mode command name, such as
+@code{c-mode}, the effect is that enabling Font Lock mode in
+@var{mode} will add @var{keywords} to @code{font-lock-keywords}.
+Calling with a non-@code{nil} value of @var{mode} is correct only in
+your @file{~/.emacs} file.
+
+If @var{mode} is @code{nil}, this function adds @var{keywords} to
+@code{font-lock-keywords} in the current buffer. This way of calling
+@code{font-lock-add-keywords} is usually used in mode hook functions.
+
+By default, @var{keywords} are added at the beginning of
+@code{font-lock-keywords}. If the optional argument @var{how} is
+@code{set}, they are used to replace the value of
+@code{font-lock-keywords}. If @var{how} is any other non-@code{nil}
+value, they are added at the end of @code{font-lock-keywords}.
+
+Some modes provide specialized support you can use in additional
+highlighting patterns. See the variables
+@code{c-font-lock-extra-types}, @code{c++-font-lock-extra-types},
+and @code{java-font-lock-extra-types}, for example.
+
+@strong{Warning:} major mode functions must not call
+@code{font-lock-add-keywords} under any circumstances, either directly
+or indirectly, except through their mode hooks. (Doing so would lead
+to incorrect behavior for some minor modes.) They should set up their
+rules for search-based fontification by setting
+@code{font-lock-keywords}.
+@end defun
-@defvar font-lock-beginning-of-syntax-function
-If this variable is non-@code{nil}, it should be a function to move
-point back to a position that is syntactically at ``top level'' and
-outside of strings or comments. Font Lock uses this when necessary
-to get the right results for syntactic fontification.
+@defun font-lock-remove-keywords mode keywords
+This function removes @var{keywords} from @code{font-lock-keywords}
+for the current buffer or for major mode @var{mode}. As in
+@code{font-lock-add-keywords}, @var{mode} should be a major mode
+command name or @code{nil}. All the caveats and requirements for
+@code{font-lock-add-keywords} apply here too.
+@end defun
-This function is called with no arguments. It should leave point at the
-beginning of any enclosing syntactic block. Typical values are
-@code{beginning-of-line} (i.e., the start of the line is known to be
-outside a syntactic block), or @code{beginning-of-defun} for programming
-modes or @code{backward-paragraph} for textual modes (i.e., the
-mode-dependent function is known to move outside a syntactic block).
+ For example, this code
-If the value is @code{nil}, the beginning of the buffer is used as a
-position outside of a syntactic block. This cannot be wrong, but it can
-be slow.
-@end defvar
+@smallexample
+(font-lock-add-keywords 'c-mode
+ '(("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend)
+ ("\\<\\(and\\|or\\|not\\)\\>" . font-lock-keyword-face)))
+@end smallexample
+
+@noindent
+adds two fontification patterns for C mode: one to fontify the word
+@samp{FIXME}, even in comments, and another to fontify the words
+@samp{and}, @samp{or} and @samp{not} as keywords.
+
+@noindent
+That example affects only C mode proper. To add the same patterns to
+C mode @emph{and} all modes derived from it, do this instead:
+
+@smallexample
+(add-hook 'c-mode-hook
+ (lambda ()
+ (font-lock-add-keywords nil
+ '(("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend)
+ ("\\<\\(and\\|or\\|not\\)\\>" .
+ font-lock-keyword-face)))))
+@end smallexample
+
+@node Other Font Lock Variables
+@subsection Other Font Lock Variables
+
+ This section describes additional variables that a major mode can
+set by means of @var{other-vars} in @code{font-lock-defaults}
+(@pxref{Font Lock Basics}).
@defvar font-lock-mark-block-function
If this variable is non-@code{nil}, it should be a function that is
@end defvar
@defvar font-lock-extra-managed-props
-Additional properties (other than @code{font-lock-face}) that are
-being managed by Font Lock mode. Font Lock mode normally manages only
-the @code{font-lock-face} property; if you want it to manage others as
-well, you must specify them in a @var{facespec} in
-@code{font-lock-keywords} as well as adding them to this list.
+This variable specifies additional properties (other than
+@code{font-lock-face}) that are being managed by Font Lock mode. It
+is used by @code{font-lock-default-unfontify-region}, which normally
+only manages the @code{font-lock-face} property. If you want Font
+Lock to manage other properties as well, you must specify them in a
+@var{facespec} in @code{font-lock-keywords} as well as add them to
+this list. @xref{Search-based Fontification}.
@end defvar
-@defvar font-lock-syntactic-face-function
-A function to determine which face to use for a given syntactic
-element (a string or a comment). The function is called with one
-argument, the parse state at point returned by
-@code{parse-partial-sexp}, and should return a face. The default
-value returns @code{font-lock-comment-face} for comments and
-@code{font-lock-string-face} for strings.
+@defvar font-lock-fontify-buffer-function
+Function to use for fontifying the buffer. The default value is
+@code{font-lock-default-fontify-buffer}.
+@end defvar
-This can be used to highlighting different kinds of strings or
-comments differently. It is also sometimes abused together with
-@code{font-lock-syntactic-keywords} to highlight elements that span
-multiple lines, but this is too obscure to document in this manual.
+@defvar font-lock-unfontify-buffer-function
+Function to use for unfontifying the buffer. This is used when
+turning off Font Lock mode. The default value is
+@code{font-lock-default-unfontify-buffer}.
@end defvar
-@defvar font-lock-lines-before
-This variable specifies the number of extra lines to consider when
-refontifying the buffer after each text change. Font lock begins
-refontifying from that number of lines before the changed region. The
-default is 1, but using a larger value can be useful for coping with
-multi-line patterns.
+@defvar font-lock-fontify-region-function
+Function to use for fontifying a region. It should take two
+arguments, the beginning and end of the region, and an optional third
+argument @var{verbose}. If @var{verbose} is non-@code{nil}, the
+function should print status messages. The default value is
+@code{font-lock-default-fontify-region}.
@end defvar
+@defvar font-lock-unfontify-region-function
+Function to use for unfontifying a region. It should take two
+arguments, the beginning and end of the region. The default value is
+@code{font-lock-default-unfontify-region}.
+@end defvar
+
+@ignore
+@defvar font-lock-inhibit-thing-lock
+List of Font Lock mode related modes that should not be turned on.
+Currently, valid mode names are @code{fast-lock-mode},
+@code{jit-lock-mode} and @code{lazy-lock-mode}.
+@end defvar
+@end ignore
+
@node Levels of Font Lock
@subsection Levels of Font Lock
@code{list-buffers} and @code{occur}.
If your mode does not use any of the other machinery of Font Lock
-(i.e. it only uses the @code{font-lock-face} property), you can tell
-Emacs not to load all of font-lock.el (unless it's already loaded), by
-setting the variable @code{font-lock-core-only} to non-@code{nil} as
-part of the @code{font-lock-defaults} settings. Here is the canonical
-way to do this:
-
-@example
-(set (make-local-variable 'font-lock-defaults)
- '(nil t nil nil nil (font-lock-core-only . t)))
-@end example
+(i.e. it only uses the @code{font-lock-face} property), it should not
+set the variable @code{font-lock-defaults}. That way, it will not
+cause loading of the @file{font-lock} library.
@node Faces for Font Lock
@subsection Faces for Font Lock
@vindex font-lock-comment-face
Used (typically) for comments.
+@item font-lock-comment-delimiter-face
+@vindex font-lock-comment-delimiter-face
+Used (typically) for comments delimiters.
+
@item font-lock-doc-face
@vindex font-lock-doc-face
Used (typically) for documentation strings in the code.
@node Syntactic Font Lock
@subsection Syntactic Font Lock
+Syntactic fontification uses the syntax table to find comments and
+string constants (@pxref{Syntax Tables}). It highlights them using
+@code{font-lock-comment-face} and @code{font-lock-string-face}
+(@pxref{Faces for Font Lock}). There are several variables that
+affect syntactic fontification; you should set them by means of
+@code{font-lock-defaults} (@pxref{Font Lock Basics}).
+
+@defvar font-lock-keywords-only
+Non-@code{nil} means Font Lock should not do syntactic fontification;
+it should only fontify based on @code{font-lock-keywords}. The normal
+way for a mode to set this variable to @code{t} is with
+@var{keywords-only} in @code{font-lock-defaults}.
+@end defvar
+
+@defvar font-lock-syntax-table
+This variable holds the syntax table to use for fontification of
+comments and strings. Specify it using @var{syntax-alist} in
+@code{font-lock-defaults}.
+@end defvar
+
+@defvar font-lock-beginning-of-syntax-function
+If this variable is non-@code{nil}, it should be a function to move
+point back to a position that is syntactically at ``top level'' and
+outside of strings or comments. Font Lock uses this when necessary
+to get the right results for syntactic fontification.
+
+This function is called with no arguments. It should leave point at
+the beginning of any enclosing syntactic block. Typical values are
+@code{beginning-of-line} (used when the start of the line is known to
+be outside a syntactic block), or @code{beginning-of-defun} for
+programming modes, or @code{backward-paragraph} for textual modes.
+
+If the value is @code{nil}, Font Lock uses
+@code{syntax-begin-function} to move back outside of any comment,
+string, or sexp. This variable is semi-obsolete; we recommend setting
+@code{syntax-begin-function} instead.
+
+Specify this variable using @var{syntax-begin} in
+@code{font-lock-defaults}.
+@end defvar
+
+@defvar font-lock-syntactic-face-function
+A function to determine which face to use for a given syntactic
+element (a string or a comment). The function is called with one
+argument, the parse state at point returned by
+@code{parse-partial-sexp}, and should return a face. The default
+value returns @code{font-lock-comment-face} for comments and
+@code{font-lock-string-face} for strings.
+
+This can be used to highlighting different kinds of strings or
+comments differently. It is also sometimes abused together with
+@code{font-lock-syntactic-keywords} to highlight constructs that span
+multiple lines, but this is too esoteric to document here.
+
+Specify this variable using @var{other-vars} in
+@code{font-lock-defaults}.
+@end defvar
+
+@node Setting Syntax Properties
+@subsection Setting Syntax Properties
+
Font Lock mode can be used to update @code{syntax-table} properties
-automatically. This is useful in languages for which a single syntax
-table by itself is not sufficient.
+automatically (@pxref{Syntax Properties}). This is useful in
+languages for which a single syntax table by itself is not sufficient.
@defvar font-lock-syntactic-keywords
-This variable enables and controls syntactic Font Lock. It is
-normally set via @code{font-lock-defaults}. Its value should be a
-list of elements of this form:
+This variable enables and controls updating @code{syntax-table}
+properties by Font Lock. Its value should be a list of elements of
+this form:
@example
(@var{matcher} @var{subexp} @var{syntax} @var{override} @var{laxmatch})
sort of element of @code{font-lock-keywords},
@example
-(@var{matcher} @var{subexp} @var{facename} @var{override} @var{laxmatch})
+(@var{matcher} @var{subexp} @var{facespec} @var{override} @var{laxmatch})
@end example
-However, instead of specifying the value @var{facename} to use for the
+However, instead of specifying the value @var{facespec} to use for the
@code{face} property, it specifies the value @var{syntax} to use for
the @code{syntax-table} property. Here, @var{syntax} can be a string
(as taken by @code{modify-syntax-entry}), a syntax table, a cons cell
as @samp{foo'bar} or @samp{'fubar'}, will not be highlighted as
strings.
+Major modes normally set this variable with @var{other-vars} in
+@code{font-lock-defaults}.
+@end defvar
+
+@node Multiline Font Lock
+@subsection Multiline Font Lock Constructs
+@cindex multiline font lock
+
+ Normally, elements of @code{font-lock-keywords} should not match
+across multiple lines; that doesn't work reliably, because Font Lock
+usually scans just part of the buffer, and it can miss a multi-line
+construct that crosses the line boundary where the scan starts. (The
+scan normally starts at the beginning of a line.)
+
+ Making elements that match multiline constructs work properly has
+two aspects: correct @emph{identification} and correct
+@emph{rehighlighting}. The first means that Font Lock finds all
+multiline constructs. The second means that Font Lock will correctly
+rehighlight all the relevant text when a multiline construct is
+changed---for example, if some of the text that was previously part of
+a multiline construct ceases to be part of it. The two aspects are
+closely related, and often getting one of them to work will appear to
+make the other also work. However, for reliable results you must
+attend explicitly to both aspects.
+
+ There are two ways to ensure correct identification of multiline
+constructs:
+
+@itemize
+@item
+Place a @code{font-lock-multiline} or @code{jit-lock-defer-multiline}
+property on the construct when it is added to the buffer.
+@item
+Use @code{font-lock-fontify-region-function} hook to extend the scan
+so that the scanned text never starts or ends in the middle of a
+multiline construct.
+@end itemize
+
+ There are three ways to do rehighlighting of multiline constructs:
+
+@itemize
+@item
+Place a @code{font-lock-multiline} property on the construct. This
+will rehighlight the whole construct if any part of it is changed. In
+some cases you can do this automatically by setting the
+@code{font-lock-multiline} variable.
+@item
+Use @code{jit-lock-contextually}. This will only rehighlight the part
+of the construct that follows the actual change, and will do it after
+a short delay. This only works if the highlighting of the various
+parts of your multiline construct never depends on text in subsequent
+lines. Since @code{jit-lock-contextually} is activated by default,
+this can be an attractive solution.
+@item
+Place a @code{jit-lock-defer-multiline} property on the construct.
+This works only if @code{jit-lock-contextually} is used, but it can
+handle the case where highlighting depends on subsequent lines.
+@item
+@end itemize
+
+@menu
+* Font Lock Multiline:: Marking multiline chunks with a text property
+* Region to Fontify:: Controlling which region gets refontified
+ after a buffer change.
+@end menu
+
+@node Font Lock Multiline
+@subsubsection Font Lock Multiline
+
+ One way to ensure reliable rehighlighting of multiline Font Lock
+constructs is to put on the text property @code{font-lock-multiline}.
+It should be present and non-@code{nil} for text that is part of a
+multiline construct.
+
+ When Font Lock is about to highlight a range of text, it first
+extends the boundaries of the range as necessary so that they do not
+fall within text marked with the @code{font-lock-multiline} property.
+Then it removes any @code{font-lock-multiline} properties from the
+range, and highlights it. The highlighting specification (mostly
+@code{font-lock-keywords}) must reinstall this property each time,
+whenever it is appropriate.
+
+ @strong{Warning:} don't use the @code{font-lock-multiline} property
+on large ranges of text, because that will make rehighlighting slow.
+
+@defvar font-lock-multiline
+If the @code{font-lock-multiline} variable is set to @code{t}, Font
+Lock will try to add the @code{font-lock-multiline} property
+automatically on multiline constructs. This is not a universal
+solution, however, since it slows down Font Lock somewhat. It can
+miss some multiline constructs, or make the property larger or smaller
+than necessary.
+
+For elements whose @var{matcher} is a function, the function should
+ensure that submatch 0 covers the whole relevant multiline construct,
+even if only a small subpart will be highlighted. It is often just as
+easy to add the @code{font-lock-multiline} property by hand.
+@end defvar
+
+ The @code{font-lock-multiline} property is meant to ensure proper
+refontification; it does not automatically identify new multiline
+constructs. Identifying the requires that Font-Lock operate on large
+enough chunks at a time. This will happen by accident on many cases,
+which may give the impression that multiline constructs magically work.
+If you set the @code{font-lock-multiline} variable non-@code{nil},
+this impression will be even stronger, since the highlighting of those
+constructs which are found will be properly updated from then on.
+But that does not work reliably.
+
+ To find multiline constructs reliably, you must either manually
+place the @code{font-lock-multiline} property on the text before
+Font-Lock looks at it, or use
+@code{font-lock-fontify-region-function}.
+
+@node Region to Fontify
+@subsubsection Region to Fontify after a Buffer Change
+
+ When a buffer is changed, the region that Font Lock refontifies is
+by default the smallest sequence of whole lines that spans the change.
+While this works well most of the time, sometimes it doesn't---for
+example, when a change alters the syntactic meaning of text on an
+earlier line.
+
+ You can enlarge (or even reduce) the region to fontify by setting
+one the following variables:
+
+@defvar font-lock-extend-region-function
+This buffer-local variable is either @code{nil} or a function for
+Font-Lock to call to determine the region to scan and fontify.
+
+The function is given three parameters, the standard @var{beg},
+@var{end}, and @var{old-len} from after-change-functions
+(@pxref{Change Hooks}). It should return either a cons of the
+beginning and end buffer positions (in that order) of the region to
+fontify, or @code{nil} (which means choose the region in the standard
+way). This function needs to preserve point, the match-data, and the
+current restriction. The region it returns may start or end in the
+middle of a line.
+
+Since this function is called after every buffer change, it should be
+reasonably fast.
@end defvar
@node Desktop Save Mode
and it should return the restored buffer.
Here @var{desktop-buffer-misc} is the value returned by the function
optionally bound to @code{desktop-save-buffer}.
-
@end defvar
-@node Hooks
-@section Hooks
-@cindex hooks
-
- A @dfn{hook} is a variable where you can store a function or functions
-to be called on a particular occasion by an existing program. Emacs
-provides hooks for the sake of customization. Most often, hooks are set
-up in the init file (@pxref{Init File}), but Lisp programs can set them also.
-@xref{Standard Hooks}, for a list of standard hook variables.
-
-@cindex normal hook
- Most of the hooks in Emacs are @dfn{normal hooks}. These variables
-contain lists of functions to be called with no arguments. When the
-hook name ends in @samp{-hook}, that tells you it is normal. We try to
-make all hooks normal, as much as possible, so that you can use them in
-a uniform way.
-
- Every major mode function is supposed to run a normal hook called the
-@dfn{mode hook} as the last step of initialization. This makes it easy
-for a user to customize the behavior of the mode, by overriding the
-buffer-local variable assignments already made by the mode. But hooks
-are used in other contexts too. For example, the hook
-@code{suspend-hook} runs just before Emacs suspends itself
-(@pxref{Suspending Emacs}).
-
- The recommended way to add a hook function to a normal hook is by
-calling @code{add-hook} (see below). The hook functions may be any of
-the valid kinds of functions that @code{funcall} accepts (@pxref{What
-Is a Function}). Most normal hook variables are initially void;
-@code{add-hook} knows how to deal with this. You can add hooks either
-globally or buffer-locally with @code{add-hook}.
-
-@cindex abnormal hook
- If the hook variable's name does not end with @samp{-hook}, that
-indicates it is probably an @dfn{abnormal hook}. Then you should look at its
-documentation to see how to use the hook properly.
-
- If the variable's name ends in @samp{-functions} or @samp{-hooks},
-then the value is a list of functions, but it is abnormal in that either
-these functions are called with arguments or their values are used in
-some way. You can use @code{add-hook} to add a function to the list,
-but you must take care in writing the function. (A few of these
-variables, notably those ending in @samp{-hooks}, are actually
-normal hooks which were named before we established the convention of
-using @samp{-hook} for them.)
-
- If the variable's name ends in @samp{-function}, then its value
-is just a single function, not a list of functions.
-
- Here's an example that uses a mode hook to turn on Auto Fill mode when
-in Lisp Interaction mode:
-
-@example
-(add-hook 'lisp-interaction-mode-hook 'turn-on-auto-fill)
-@end example
-
- At the appropriate time, Emacs uses the @code{run-hooks} function to
-run particular hooks. This function calls the hook functions that have
-been added with @code{add-hook}.
-
-@defun run-hooks &rest hookvars
-This function takes one or more normal hook variable names as
-arguments, and runs each hook in turn. Each argument should be a
-symbol that is a normal hook variable. These arguments are processed
-in the order specified.
-
-If a hook variable has a non-@code{nil} value, that value may be a
-function or a list of functions. (The former option is considered
-obsolete.) If the value is a function (either a lambda expression or
-a symbol with a function definition), it is called. If it is a list
-that isn't a function, its elements are called, consecutively. All
-the hook functions are called with no arguments.
-@end defun
-
-@defun run-hook-with-args hook &rest args
-This function is the way to run an abnormal hook and always call all
-of the hook functions. It calls each of the hook functions one by
-one, passing each of them the arguments @var{args}.
-@end defun
-
-@defun run-hook-with-args-until-failure hook &rest args
-This function is the way to run an abnormal hook until one of the hook
-functions fails. It calls each of the hook functions, passing each of
-them the arguments @var{args}, until some hook function returns
-@code{nil}. It then stops and returns @code{nil}. If none of the
-hook functions return @code{nil}, it returns a non-@code{nil} value.
-@end defun
-
-@defun run-hook-with-args-until-success hook &rest args
-This function is the way to run an abnormal hook until a hook function
-succeeds. It calls each of the hook functions, passing each of them
-the arguments @var{args}, until some hook function returns
-non-@code{nil}. Then it stops, and returns whatever was returned by
-the last hook function that was called. If all hook functions return
-@code{nil}, it returns @code{nil} as well.
-@end defun
-
-@defun add-hook hook function &optional append local
-This function is the handy way to add function @var{function} to hook
-variable @var{hook}. You can use it for abnormal hooks as well as for
-normal hooks. @var{function} can be any Lisp function that can accept
-the proper number of arguments for @var{hook}. For example,
-
-@example
-(add-hook 'text-mode-hook 'my-text-hook-function)
-@end example
-
-@noindent
-adds @code{my-text-hook-function} to the hook called @code{text-mode-hook}.
-
-If @var{function} is already present in @var{hook} (comparing using
-@code{equal}), then @code{add-hook} does not add it a second time.
-
-It is best to design your hook functions so that the order in which they
-are executed does not matter. Any dependence on the order is ``asking
-for trouble''. However, the order is predictable: normally,
-@var{function} goes at the front of the hook list, so it will be
-executed first (barring another @code{add-hook} call). If the optional
-argument @var{append} is non-@code{nil}, the new hook function goes at
-the end of the hook list and will be executed last.
-
-If @var{local} is non-@code{nil}, that says to add @var{function} to
-the buffer-local hook list instead of to the global hook list. If
-needed, this makes the hook buffer-local and adds @code{t} to the
-buffer-local value. The latter acts as a flag to run the hook
-functions in the default value as well as in the local value.
-@end defun
-
-@defun remove-hook hook function &optional local
-This function removes @var{function} from the hook variable
-@var{hook}. It compares @var{function} with elements of @var{hook}
-using @code{equal}, so it works for both symbols and lambda
-expressions.
-
-If @var{local} is non-@code{nil}, that says to remove @var{function}
-from the buffer-local hook list instead of from the global hook list.
-@end defun
-
@ignore
arch-tag: 4c7bff41-36e6-4da6-9e7f-9b9289e27c8e
@end ignore