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A mode is a set of definitions that customize XEmacs and can be turned on and off while you edit. There are two varieties of modes: major modes, which are mutually exclusive and used for editing particular kinds of text, and minor modes, which provide features that users can enable individually.
This chapter describes how to write both major and minor modes, how to indicate them in the modeline, and how they run hooks supplied by the user. For related topics such as keymaps and syntax tables, see Keymaps, and Syntax Tables.
33.1 Major Modes | Defining major modes. | |
33.2 Minor Modes | Defining minor modes. | |
33.3 Modeline Format | Customizing the text that appears in the modeline. | |
33.4 Hooks | How to use hooks; how to write code that provides hooks. |
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Major modes specialize XEmacs for editing particular kinds of text. Each buffer has only one major mode at a time. For each major mode there is a function to switch to that mode in the current buffer; its name should end in ‘-mode’. These functions work by setting buffer-local variable bindings and other data associated with the buffer, such as a local keymap. The effect lasts until you switch to another major mode in the same buffer.
The least specialized major mode is called Fundamental mode.
This mode has no mode-specific definitions or variable settings, so each
XEmacs command behaves in its default manner, and each option is in its
default state. All other major modes redefine various keys and options.
For example, Lisp Interaction mode provides special key bindings for
<LFD> (eval-print-last-sexp
), <TAB>
(lisp-indent-line
), and other keys.
When you need to write several editing commands to help you perform a specialized editing task, creating a new major mode is usually a good idea. In practice, writing a major mode is easy (in contrast to writing a minor mode, which is often difficult).
If the new mode is similar to an old one, it is often unwise to modify the old one to serve two purposes, since it may become harder to use and maintain. Instead, copy and rename an existing major mode definition and alter the copy—or define a derived mode (see section Defining Derived Modes). For example, Rmail Edit mode, which is in ‘emacs/lisp/rmailedit.el’, is a major mode that is very similar to Text mode except that it provides three additional commands. Its definition is distinct from that of Text mode, but was derived from it.
Even if the new mode is not an obvious derivative of any other mode,
it is convenient to use define-derived-mode
with a nil
parent argument, since it automatically enforces the most important
coding conventions for you.
Rmail Edit mode is an example of a case where one piece of text is put temporarily into a different major mode so it can be edited in a different way (with ordinary XEmacs commands rather than Rmail). In such cases, the temporary major mode usually has a command to switch back to the buffer’s usual mode (Rmail mode, in this case). You might be tempted to present the temporary redefinitions inside a recursive edit and restore the usual ones when the user exits; but this is a bad idea because it constrains the user’s options when it is done in more than one buffer: recursive edits must be exited most-recently-entered first. Using alternative major modes avoids this limitation. See section Recursive Editing.
The standard XEmacs Lisp library directory contains the code for several major modes, in files including ‘text-mode.el’, ‘texinfo.el’, ‘lisp-mode.el’, ‘c-mode.el’, and ‘rmail.el’. You can look at these libraries to see how modes are written. Text mode is perhaps the simplest major mode aside from Fundamental mode. Rmail mode is a complicated and specialized mode.
33.1.1 Major Mode Conventions | Coding conventions for keymaps, etc. | |
33.1.2 Major Mode Examples | Text mode and Lisp modes. | |
33.1.3 How XEmacs Chooses a Major Mode | How XEmacs chooses the major mode automatically. | |
33.1.4 Getting Help about a Major Mode | Finding out how to use a mode. | |
33.1.5 Defining Derived Modes | Defining a new major mode based on another major mode. |
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The code for existing major modes follows various coding conventions, including conventions for local keymap and syntax table initialization, global names, and hooks. Please follow these conventions when you define a new major mode:
describe-mode
) in your mode will display this string.
The documentation string may include the special documentation substrings, ‘\[command]’, ‘\{keymap}’, and ‘\<keymap>’, that enable the documentation to adapt automatically to the user’s own key bindings. See section Substituting Key Bindings in Documentation.
kill-all-local-variables
. This is what gets rid of the local
variables of the major mode previously in effect.
major-mode
to the
major mode command symbol. This is how describe-mode
discovers
which documentation to print.
mode-name
to the
“pretty” name of the mode, as a string. This appears in the mode
line.
use-local-map
to install this local map.
See section Active Keymaps, for more information.
This keymap should be kept in a global variable named
modename-mode-map
. Normally the library that defines the
mode sets this variable.
modename-mode-syntax-table
. See section Syntax Tables.
modename-mode-abbrev-table
. See section Abbrev Tables.
defvar
to set mode-related variables, so that they are not
reinitialized if they already have a value. (Such reinitialization
could discard customizations made by the user.)
make-local-variable
in the major mode command, not
make-variable-buffer-local
. The latter function would make the
variable local to every buffer in which it is subsequently set, which
would affect buffers that do not use this mode. It is undesirable for a
mode to have such global effects. See section Buffer-Local Variables.
It’s ok to use make-variable-buffer-local
, if you wish, for a
variable used only within a single Lisp package.
modename-mode-hook
. The major mode command should run that
hook, with run-hooks
, as the very last thing it
does. See section Hooks.
indented-text-mode
runs text-mode-hook
as
well as indented-text-mode-hook
. It may run these other hooks
immediately before the mode’s own hook (that is, after everything else),
or it may run them earlier.
define-derived-mode
,
but this is not required. Such a mode should use
delay-mode-hooks
around its entire body, including the call to
the parent mode command and the final call to run-mode-hooks
.
(Using define-derived-mode
does this automatically.)
change-major-mode-hook
.
mode-class
with value special
, put on as follows:
(put 'funny-mode 'mode-class 'special) |
This tells XEmacs that new buffers created while the current buffer has Funny mode should not inherit Funny mode. Modes such as Dired, Rmail, and Buffer List use this feature.
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
autoload
. Otherwise, it is sufficient to add the element in the
file that contains the mode definition. See section How XEmacs Chooses a Major Mode.
autoload
form
and an example of how to add to auto-mode-alist
, that users can
include in their ‘.emacs’ files.
This normal hook is run by kill-all-local-variables
before it
does anything else. This gives major modes a way to arrange for
something special to be done if the user switches to a different major
mode. For best results, make this variable buffer-local, so that it
will disappear after doing its job and will not interfere with the
subsequent major mode. See section Hooks.
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Text mode is perhaps the simplest mode besides Fundamental mode. Here are excerpts from ‘text-mode.el’ that illustrate many of the conventions listed above:
;; Create mode-specific tables.
(defvar text-mode-syntax-table nil
"Syntax table used while in text mode.")
(if text-mode-syntax-table
() ; Do not change the table if it is already set up.
(setq text-mode-syntax-table (make-syntax-table))
(modify-syntax-entry ?\" ". " text-mode-syntax-table)
(modify-syntax-entry ?\\ ". " text-mode-syntax-table)
(modify-syntax-entry ?' "w " text-mode-syntax-table))
(defvar text-mode-abbrev-table nil "Abbrev table used while in text mode.") (define-abbrev-table 'text-mode-abbrev-table ()) (defvar text-mode-map nil) ; Create a mode-specific keymap. (if text-mode-map () ; Do not change the keymap if it is already set up. (setq text-mode-map (make-sparse-keymap)) (define-key text-mode-map "\t" 'tab-to-tab-stop) (define-key text-mode-map "\es" 'center-line) (define-key text-mode-map "\eS" 'center-paragraph)) |
Here is the complete major mode function definition for Text mode:
(defun text-mode () "Major mode for editing text intended for humans to read. Special commands: \\{text-mode-map} Turning on text-mode runs the hook `text-mode-hook'." (interactive) (kill-all-local-variables) (use-local-map text-mode-map) ; This provides the local keymap.
(setq mode-name "Text") ; This name goes into the modeline.
(setq major-mode 'text-mode) ; This is how |
The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp Interaction mode) have more features than Text mode and the code is correspondingly more complicated. Here are excerpts from ‘lisp-mode.el’ that illustrate how these modes are written.
;; Create mode-specific table variables.
(defvar lisp-mode-syntax-table nil "")
(defvar emacs-lisp-mode-syntax-table nil "")
(defvar lisp-mode-abbrev-table nil "")
(if (not emacs-lisp-mode-syntax-table) ; Do not change the table ; if it is already set. (let ((i 0)) (setq emacs-lisp-mode-syntax-table (make-syntax-table)) ;; Set syntax of chars up to 0 to class of chars that are
;; part of symbol names but not words.
;; (The number 0 is ;; Set the syntax for other characters.
(modify-syntax-entry ? " " emacs-lisp-mode-syntax-table)
(modify-syntax-entry ?\t " " emacs-lisp-mode-syntax-table)
…
(modify-syntax-entry ?\( "() " emacs-lisp-mode-syntax-table)
(modify-syntax-entry ?\) ")( " emacs-lisp-mode-syntax-table)
…))
;; Create an abbrev table for lisp-mode.
(define-abbrev-table 'lisp-mode-abbrev-table ())
|
Much code is shared among the three Lisp modes. The following function sets various variables; it is called by each of the major Lisp mode functions:
(defun lisp-mode-variables (lisp-syntax) ;; The (progn (setq lisp-mode-syntax-table
(copy-syntax-table emacs-lisp-mode-syntax-table))
;; Change some entries for Lisp mode.
(modify-syntax-entry ?\| "\" "
lisp-mode-syntax-table)
(modify-syntax-entry ?\[ "_ "
lisp-mode-syntax-table)
(modify-syntax-entry ?\] "_ "
lisp-mode-syntax-table)))
(set-syntax-table lisp-mode-syntax-table))) (setq local-abbrev-table lisp-mode-abbrev-table) …) |
Functions such as forward-paragraph
use the value of the
paragraph-start
variable. Since Lisp code is different from
ordinary text, the paragraph-start
variable needs to be set
specially to handle Lisp. Also, comments are indented in a special
fashion in Lisp and the Lisp modes need their own mode-specific
comment-indent-function
. The code to set these variables is the
rest of lisp-mode-variables
.
(make-local-variable 'paragraph-start)
;; Having ‘^’ is not clean, but (make-local-variable 'comment-indent-function) (setq comment-indent-function 'lisp-comment-indent)) |
Each of the different Lisp modes has a slightly different keymap. For
example, Lisp mode binds C-c C-l to run-lisp
, but the other
Lisp modes do not. However, all Lisp modes have some commands in
common. The following function adds these common commands to a given
keymap.
(defun lisp-mode-commands (map) (define-key map "\e\C-q" 'indent-sexp) (define-key map "\177" 'backward-delete-char-untabify) (define-key map "\t" 'lisp-indent-line)) |
Here is an example of using lisp-mode-commands
to initialize a
keymap, as part of the code for Emacs Lisp mode. First we declare a
variable with defvar
to hold the mode-specific keymap. When this
defvar
executes, it sets the variable to nil
if it was
void. Then we set up the keymap if the variable is nil
.
This code avoids changing the keymap or the variable if it is already set up. This lets the user customize the keymap.
(defvar emacs-lisp-mode-map () "") (if emacs-lisp-mode-map () (setq emacs-lisp-mode-map (make-sparse-keymap)) (define-key emacs-lisp-mode-map "\e\C-x" 'eval-defun) (lisp-mode-commands emacs-lisp-mode-map)) |
Finally, here is the complete major mode function definition for Emacs Lisp mode.
(defun emacs-lisp-mode () "Major mode for editing Lisp code to run in XEmacs. Commands: Delete converts tabs to spaces as it moves back. Blank lines separate paragraphs. Semicolons start comments. \\{emacs-lisp-mode-map} Entry to this mode runs the hook `emacs-lisp-mode-hook'."
(interactive)
(kill-all-local-variables)
(use-local-map emacs-lisp-mode-map) ; This provides the local keymap.
(set-syntax-table emacs-lisp-mode-syntax-table)
(setq major-mode 'emacs-lisp-mode) ; This is how |
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Based on information in the file name or in the file itself, XEmacs automatically selects a major mode for the new buffer when a file is visited.
Fundamental mode is a major mode that is not specialized for anything
in particular. Other major modes are defined in effect by comparison
with this one—their definitions say what to change, starting from
Fundamental mode. The fundamental-mode
function does not
run any hooks; you’re not supposed to customize it. (If you want Emacs
to behave differently in Fundamental mode, change the global
state of Emacs.)
This function establishes the proper major mode and local variable
bindings for the current buffer. First it calls set-auto-mode
,
then it runs hack-local-variables
to parse, and bind or
evaluate as appropriate, any local variables.
If the find-file argument to normal-mode
is
non-nil
, normal-mode
assumes that the 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 ‘-*-’ line. The variable
enable-local-variables
controls whether to do so.
If you run normal-mode
interactively, the argument
find-file is normally nil
. In this case,
normal-mode
unconditionally processes any local variables list.
See (xemacs)File variables section ‘Local Variables in Files’ in The XEmacs Reference Manual, for the syntax of the local variables section of a file.
normal-mode
uses condition-case
around the call to the
major mode function, so errors are caught and reported as a ‘File
mode specification error’, followed by the original error message.
This variable controls processing of local variables lists in files
being visited. A value of t
means process the local variables
lists unconditionally; nil
means ignore them; anything else means
ask the user what to do for each file. The default value is t
.
This variable holds a list of variables that should not be set by a local variables list. Any value specified for one of these variables is ignored.
In addition to this list, any variable whose name has a non-nil
risky-local-variable
property is also ignored.
This variable controls processing of ‘Eval:’ in local variables
lists in files being visited. A value of t
means process them
unconditionally; nil
means ignore them; anything else means ask
the user what to do for each file. The default value is maybe
.
This function selects the major mode that is appropriate for the
current buffer. It may base its decision on the value of the ‘-*-’
line, on the visited file name (using auto-mode-alist
), or on the
value of a local variable. However, this function does not look for
the ‘mode:’ local variable near the end of a file; the
hack-local-variables
function does that. See (xemacs)Choosing Modes section ‘How Major Modes are Chosen’ in The XEmacs Lisp Reference Manual.
This variable holds the default major mode for new buffers. The
standard value is fundamental-mode
.
If the value of default-major-mode
is nil
, XEmacs uses
the (previously) current buffer’s major mode for the major mode of a new
buffer. However, if the major mode symbol has a mode-class
property with value 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
been specially prepared.
This function sets the major mode of buffer to the value of
default-major-mode
. If that variable is nil
, it uses
the current buffer’s major mode (if that is suitable).
The low-level primitives for creating buffers do not use this function,
but medium-level commands such as switch-to-buffer
and
find-file-noselect
use it whenever they create buffers.
The value of this variable determines the major mode of the initial
‘*scratch*’ buffer. The value should be a symbol that is a major
mode command name. The default value is lisp-interaction-mode
.
This variable contains an association list of file name patterns
(regular expressions; see section Regular Expressions) and corresponding
major mode functions. Usually, the file name patterns test for
suffixes, such as ‘.el’ and ‘.c’, but this need not be the
case. An ordinary element of the alist looks like (regexp .
mode-function)
.
For example,
(("^/tmp/fol/" . text-mode) ("\\.texinfo\\'" . texinfo-mode) ("\\.texi\\'" . texinfo-mode) ("\\.el\\'" . emacs-lisp-mode) ("\\.c\\'" . c-mode) ("\\.h\\'" . c-mode) …) |
When you visit a file whose expanded file name (see section Functions that Expand Filenames) matches a regexp, set-auto-mode
calls the
corresponding mode-function. This feature enables XEmacs to select
the proper major mode for most files.
If an element of auto-mode-alist
has the form (regexp
function t)
, then after calling function, XEmacs searches
auto-mode-alist
again for a match against the portion of the file
name that did not match before.
This match-again feature is useful for uncompression packages: an entry
of the form ("\\.gz\\'" . function)
can uncompress the file
and then put the uncompressed file in the proper mode according to the
name sans ‘.gz’.
Here is an example of how to prepend several pattern pairs to
auto-mode-alist
. (You might use this sort of expression in your
‘.emacs’ file.)
(setq auto-mode-alist (append ;; File name starts with a dot. '(("/\\.[^/]*\\'" . fundamental-mode) ;; File name has no dot. ("[^\\./]*\\'" . fundamental-mode) ;; File name ends in ‘.C’. ("\\.C\\'" . c++-mode)) auto-mode-alist)) |
This variable specifies major modes to use for scripts that specify a
command interpreter in an ‘#!’ line. Its value is a list of
elements of the form (interpreter . mode)
; for
example, ("perl" . perl-mode)
is one element present by default.
The element says to use mode mode if the file specifies
interpreter.
This variable is applicable only when the auto-mode-alist
does
not indicate which major mode to use.
This function parses, and binds or evaluates as appropriate, any local variables for the current buffer.
The handling of enable-local-variables
documented for
normal-mode
actually takes place here. The argument force
usually comes from the argument find-file given to
normal-mode
.
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The describe-mode
function is used to provide information
about major modes. It is normally called with C-h m. The
describe-mode
function uses the value of major-mode
,
which is why every major mode function needs to set the
major-mode
variable.
This function displays the documentation of the current major mode.
The describe-mode
function calls the documentation
function using the value of major-mode
as an argument. Thus, it
displays the documentation string of the major mode function.
(See section Access to Documentation Strings.)
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 describe-mode
function uses the
documentation string of the function as the documentation of the major
mode.
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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 define-derived-mode
.
This construct defines variant as a major mode command, using name as the string form of the mode name.
The new command variant is defined to call the function parent, then override certain aspects of that parent mode:
variant-map
.
define-derived-mode
initializes this map to inherit from
parent-map
, if it is not already set.
variant-syntax-table
.
define-derived-mode
initializes this variable by copying
parent-syntax-table
, if it is not already set.
variant-abbrev-table
.
define-derived-mode
initializes this variable by copying
parent-abbrev-table
, if it is not already set.
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 parent as part
of calling parent.)
In addition, you can specify how to override other aspects of
parent with body. The command variant
evaluates the forms in body after setting up all its usual
overrides, just before running variant-hook
.
The argument docstring specifies the documentation string for the
new mode. If you omit docstring, define-derived-mode
generates a documentation string.
Here is a hypothetical example:
(define-derived-mode hypertext-mode text-mode "Hypertext" "Major mode for hypertext. \\{hypertext-mode-map}" (setq case-fold-search nil)) (define-key hypertext-mode-map [down-mouse-3] 'do-hyper-link) |
Do not write an interactive
spec in the definition;
define-derived-mode
does that automatically.
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A minor mode provides features that users may enable or disable independently of the choice of major mode. Minor modes can be enabled individually or in combination. Minor modes would be better named “Generally available, optional feature modes” except that such a name is unwieldy.
A minor mode is not usually a modification of single major mode. For example, Auto Fill mode may be used in any major mode that permits text insertion. To be general, a minor mode must be effectively independent of the things major modes do.
A minor mode is often much more difficult to implement than a major mode. One reason is that you should be able to activate and deactivate minor modes in any order. A minor mode should be able to have its desired effect regardless of the major mode and regardless of the other minor modes in effect.
Often the biggest problem in implementing a minor mode is finding a way to insert the necessary hook into the rest of XEmacs. Minor mode keymaps make this easier than it used to be.
33.2.1 Conventions for Writing Minor Modes | Tips for writing a minor mode. | |
33.2.2 Keymaps and Minor Modes | How a minor mode can have its own keymap. |
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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.
In addition, there are several conventions that are specific to minor modes.
nil
to
disable; anything else to enable.) We call this the mode
variable.
This variable is used in conjunction with the minor-mode-alist
to
display the minor mode name in the modeline. It can also enable
or disable a minor mode keymap. Individual commands or hooks can also
check the variable’s value.
If you want the minor mode to be enabled separately in each buffer, make the variable buffer-local.
The command should accept one optional argument. If the argument is
nil
, it should toggle the mode (turn it on if it is off, and off
if it is on). Otherwise, it should turn the mode on if the argument is
a positive integer, a symbol other than nil
or -
, or a
list whose CAR is such an integer or symbol; it should turn the
mode off otherwise.
Here is an example taken from the definition of transient-mark-mode
.
It shows the use of transient-mark-mode
as a variable that enables or
disables the mode’s behavior, and also shows the proper way to toggle,
enable or disable the minor mode based on the raw prefix argument value.
(setq transient-mark-mode (if (null arg) (not transient-mark-mode) (> (prefix-numeric-value arg) 0))) |
minor-mode-alist
for each minor mode
(see section Variables Used in the Modeline). This element should be a list of the
following form:
(mode-variable string) |
Here mode-variable is the variable that controls enabling of the minor mode, and string is a short string, starting with a space, to represent the mode in the modeline. These strings must be short so that there is room for several of them at once.
When you add an element to minor-mode-alist
, use assq
to
check for an existing element, to avoid duplication. For example:
(or (assq 'leif-mode minor-mode-alist) (setq minor-mode-alist (cons '(leif-mode " Leif") minor-mode-alist))) |
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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 minor-mode-map-alist
. See section Active Keymaps.
One use of minor mode keymaps is to modify the behavior of certain
self-inserting characters so that they do something else as well as
self-insert. In general, this is the only way to do that, since the
facilities for customizing self-insert-command
are limited to
special cases (designed for abbrevs and Auto Fill mode). (Do not try
substituting your own definition of self-insert-command
for the
standard one. The editor command loop handles this function specially.)
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Each Emacs window (aside from minibuffer windows) includes a modeline, which displays status information about the buffer displayed in the window. The modeline contains information about the buffer, such as its name, associated file, depth of recursive editing, and the major and minor modes.
This section describes how the contents of the modeline are controlled. It is in the chapter on modes because much of the information displayed in the modeline relates to the enabled major and minor modes.
modeline-format
is a buffer-local variable that holds a
template used to display the modeline of the current buffer. All
windows for the same buffer use the same modeline-format
and
their modelines appear the same (except for scrolling percentages and
line numbers).
The modeline of a window is normally updated whenever a different
buffer is shown in the window, or when the buffer’s modified-status
changes from nil
to t
or vice-versa. If you modify any of
the variables referenced by modeline-format
(see section Variables Used in the Modeline), you may want to force an update of the modeline so as to
display the new information.
Force redisplay of the current buffer’s modeline. If all is
non-nil
, then force redisplay of all modelines.
The modeline is usually displayed in inverse video. This
is controlled using the modeline
face. See section Faces.
33.3.1 The Data Structure of the Modeline | The data structure that controls the modeline. | |
33.3.2 Variables Used in the Modeline | Variables used in that data structure. | |
33.3.3 % -Constructs in the ModeLine | Putting information into a modeline. |
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The modeline contents are controlled by a data structure of lists,
strings, symbols, and numbers kept in the buffer-local variable
modeline-format
. The data structure is called a modeline
construct, and it is built in recursive fashion out of simpler modeline
constructs. The same data structure is used for constructing
frame titles (see section Frame Titles).
The value of this variable is a modeline construct with overall responsibility for the modeline format. The value of this variable controls which other variables are used to form the modeline text, and where they appear.
A modeline 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 modeline constructs as their values.
The default value of modeline-format
incorporates the values
of variables such as mode-name
and minor-mode-alist
.
Because of this, very few modes need to alter modeline-format
.
For most purposes, it is sufficient to alter the variables referenced by
modeline-format
.
A modeline construct may be a string, symbol, glyph, generic specifier, list or cons cell.
string
A string as a modeline construct is displayed verbatim in the mode line
except for %
-constructs. Decimal digits after the ‘%’
specify the field width for space filling on the right (i.e., the data
is left justified). See section %
-Constructs in the ModeLine.
symbol
A symbol as a modeline construct stands for its value. The value of
symbol is processed as a modeline construct, in place of
symbol. However, the symbols t
and nil
are ignored;
so is any symbol whose value is void.
There is one exception: if the value of symbol is a string, it is
displayed verbatim: the %
-constructs are not recognized.
glyph
A glyph is displayed as is.
generic-specifier
A generic-specifier (i.e. a specifier of type generic
)
stands for its instance. The instance of generic-specifier is
computed in the current window using the equivalent of
specifier-instance
and the value is processed.
(string rest…) or (list rest…)
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.
(symbol then else)
A list whose first element is a symbol is a conditional. Its meaning
depends on the value of symbol. If the value is non-nil
,
the second element, then, is processed recursively as a modeline
element. But if the value of symbol is nil
, the third
element, else, is processed recursively. You may omit else;
then the mode line element displays nothing if the value of symbol
is nil
.
(width rest…)
A list whose first element is an integer specifies truncation or padding of the results of rest. The remaining elements rest are processed recursively as modeline constructs and concatenated together. Then the result is space filled (if width is positive) or truncated (to -width columns, if width is negative) on the right.
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: (-3 "%p")
.
(extent rest…)
A list whose car is an extent means the cdr of the list is processed normally but the results are displayed using the face of the extent, and mouse clicks over this section are processed using the keymap of the extent. (In addition, if the extent has a help-echo property, that string will be echoed when the mouse moves over this section.) If extents are nested, all keymaps are properly consulted when processing mouse clicks, but multiple faces are not correctly merged (only the first face is used), and lists of faces are not correctly handled.
If you do alter modeline-format
itself, the new value should
use the same variables that appear in the default value (see section Variables Used in the Modeline), rather than duplicating their contents or displaying
the information in another fashion. This way, customizations made by
the user or by Lisp programs (such as display-time
and major
modes) via changes to those variables remain effective.
Here is an example of a modeline-format
that might be
useful for shell-mode
, since it contains the hostname and default
directory.
(setq modeline-format (list "" 'modeline-modified "%b--" (getenv "HOST") ; One element is not constant.
":"
'default-directory
" "
'global-mode-string
" %[("
'mode-name
'modeline-process
'minor-mode-alist
"%n"
")%]----"
'(line-number-mode "L%l--") '(-3 . "%p") "-%-")) |
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This section describes variables incorporated by the
standard value of modeline-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 modeline if
modeline-format
were changed to use them.
This variable holds the value of the modeline construct that displays whether the current buffer is modified.
The default value of modeline-modified
is ("--%1*%1+-")
.
This means that the modeline displays ‘--**-’ if the buffer is
modified, ‘-----’ if the buffer is not modified, ‘--%%-’ if
the buffer is read only, and ‘--%*--’ if the buffer is read only
and modified.
Changing this variable does not force an update of the modeline.
This variable identifies the buffer being displayed in the window. Its
default value is ("%F: %17b")
, which means that it usually
displays ‘Emacs:’ followed by seventeen characters of the buffer
name. (In a terminal frame, it displays the frame name instead of
‘Emacs’; this has the effect of showing the frame number.) You may
want to change this in modes such as Rmail that do not behave like a
“normal” XEmacs.
This variable holds a modeline spec that appears in the mode line by
default, just after the buffer name. The command display-time
sets global-mode-string
to refer to the variable
display-time-string
, which holds a string containing the time and
load information.
The ‘%M’ construct substitutes the value of
global-mode-string
, but this is obsolete, since the variable is
included directly in the modeline.
This buffer-local variable holds the “pretty” name of the current buffer’s major mode. Each major mode should set this variable so that the mode name will appear in the modeline.
This variable holds an association list whose elements specify how the
modeline should indicate that a minor mode is active. Each element of
the minor-mode-alist
should be a two-element list:
(minor-mode-variable modeline-string) |
More generally, modeline-string can be any mode line spec. It
appears in the mode line when the value of minor-mode-variable is
non-nil
, and not otherwise. These strings should begin with
spaces so that they don’t run together. Conventionally, the
minor-mode-variable for a specific mode is set to a non-nil
value when that minor mode is activated.
The default value of minor-mode-alist
is:
minor-mode-alist ⇒ ((vc-mode vc-mode) (abbrev-mode " Abbrev") (overwrite-mode overwrite-mode) (auto-fill-function " Fill") (defining-kbd-macro " Def") (isearch-mode isearch-mode)) |
minor-mode-alist
is not buffer-local. The variables mentioned
in the alist should be buffer-local if the minor mode can be enabled
separately in each buffer.
This buffer-local variable contains the modeline information on process
status in modes used for communicating with subprocesses. It is
displayed immediately following the major mode name, with no intervening
space. For example, its value in the ‘*shell*’ buffer is
(": %s")
, which allows the shell to display its status along
with the major mode as: ‘(Shell: run)’. Normally this variable
is nil
.
This variable holds the default modeline-format
for buffers
that do not override it. This is the same as (default-value
'modeline-format)
.
The default value of default-modeline-format
is:
("" modeline-modified modeline-buffer-identification " " global-mode-string " %[(" mode-name modeline-process minor-mode-alist "%n" ")%]----" (line-number-mode "L%l--") (-3 . "%p") "-%-") |
The variable vc-mode
, local in each buffer, records whether the
buffer’s visited file is maintained with version control, and, if so,
which kind. Its value is nil
for no version control, or a string
that appears in the mode line.
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%
-Constructs in the ModeLine The following table lists the recognized %
-constructs and what
they mean. In any construct except ‘%%’, you can add a decimal
integer after the ‘%’ to specify how many characters to display.
%b
The current buffer name, obtained with the buffer-name
function.
See section Buffer Names.
%f
The visited file name, obtained with the buffer-file-name
function. See section Buffer File Name.
%F
The name of the selected frame.
%c
The current column number of point.
%l
The current line number of point.
%*
‘%’ if the buffer is read only (see buffer-read-only
);
‘*’ if the buffer is modified (see buffer-modified-p
);
‘-’ otherwise. See section Buffer Modification.
%+
‘*’ if the buffer is modified (see buffer-modified-p
);
‘%’ if the buffer is read only (see buffer-read-only
);
‘-’ otherwise. This differs from ‘%*’ only for a modified
read-only buffer. See section Buffer Modification.
%&
‘*’ if the buffer is modified, and ‘-’ otherwise.
%s
The status of the subprocess belonging to the current buffer, obtained with
process-status
. See section Process Information.
%l
The current line number.
%S
The name of the selected frame; this is only meaningful under the X Window System. See section The Name of a Frame (As Opposed to Its Title).
%t
Whether the visited file is a text file or a binary file. (This is a meaningful distinction only on certain operating systems.)
%p
The percentage of the buffer text above the top of window, or ‘Top’, ‘Bottom’ or ‘All’.
%P
The percentage of the buffer text that is above the bottom of the window (which includes the text visible in the window, as well as the text above the top), plus ‘Top’ if the top of the buffer is visible on screen; or ‘Bottom’ or ‘All’.
%n
‘Narrow’ when narrowing is in effect; nothing otherwise (see
narrow-to-region
in Narrowing).
%C
Under XEmacs/mule, the mnemonic for buffer-file-coding-system
.
%[
An indication of the depth of recursive editing levels (not counting minibuffer levels): one ‘[’ for each editing level. See section Recursive Editing.
%]
One ‘]’ for each recursive editing level (not counting minibuffer levels).
%%
The character ‘%’—this is how to include a literal ‘%’ in a
string in which %
-constructs are allowed.
%-
Dashes sufficient to fill the remainder of the modeline.
The following two %
-constructs are still supported, but they are
obsolete, since you can get the same results with the variables
mode-name
and global-mode-string
.
%m
The value of mode-name
.
%M
The value of global-mode-string
. Currently, only
display-time
modifies the value of global-mode-string
.
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