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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
f8cecb20 | 3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2003 |
177c0ea7 | 4 | @c Free Software Foundation, Inc. |
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5 | @c See the file elisp.texi for copying conditions. |
6 | @setfilename ../info/modes | |
3ebe0346 | 7 | @node Modes, Documentation, Keymaps, Top |
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8 | @chapter Major and Minor Modes |
9 | @cindex mode | |
10 | ||
11 | A @dfn{mode} is a set of definitions that customize Emacs and can be | |
12 | turned on and off while you edit. There are two varieties of modes: | |
13 | @dfn{major modes}, which are mutually exclusive and used for editing | |
14 | particular kinds of text, and @dfn{minor modes}, which provide features | |
15 | that users can enable individually. | |
16 | ||
17 | This chapter describes how to write both major and minor modes, how to | |
18 | indicate them in the mode line, and how they run hooks supplied by the | |
19 | user. For related topics such as keymaps and syntax tables, see | |
20 | @ref{Keymaps}, and @ref{Syntax Tables}. | |
21 | ||
22 | @menu | |
23 | * Major Modes:: Defining major modes. | |
24 | * Minor Modes:: Defining minor modes. | |
25 | * Mode Line Format:: Customizing the text that appears in the mode line. | |
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26 | * Imenu:: How a mode can provide a menu |
27 | of definitions in the buffer. | |
28 | * Font Lock Mode:: How modes can highlight text according to syntax. | |
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29 | * Hooks:: How to use hooks; how to write code that provides hooks. |
30 | @end menu | |
31 | ||
32 | @node Major Modes | |
33 | @section Major Modes | |
34 | @cindex major mode | |
35 | @cindex Fundamental mode | |
36 | ||
37 | Major modes specialize Emacs for editing particular kinds of text. | |
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38 | Each buffer has only one major mode at a time. For each major mode |
39 | there is a function to switch to that mode in the current buffer; its | |
40 | name should end in @samp{-mode}. These functions work by setting | |
41 | buffer-local variable bindings and other data associated with the | |
42 | buffer, such as a local keymap. The effect lasts until you switch | |
43 | to another major mode in the same buffer. | |
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44 | |
45 | The least specialized major mode is called @dfn{Fundamental mode}. | |
46 | This mode has no mode-specific definitions or variable settings, so each | |
47 | Emacs command behaves in its default manner, and each option is in its | |
48 | default state. All other major modes redefine various keys and options. | |
49 | For example, Lisp Interaction mode provides special key bindings for | |
969fe9b5 | 50 | @kbd{C-j} (@code{eval-print-last-sexp}), @key{TAB} |
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51 | (@code{lisp-indent-line}), and other keys. |
52 | ||
53 | When you need to write several editing commands to help you perform a | |
54 | specialized editing task, creating a new major mode is usually a good | |
55 | idea. In practice, writing a major mode is easy (in contrast to | |
56 | writing a minor mode, which is often difficult). | |
57 | ||
58 | If the new mode is similar to an old one, it is often unwise to modify | |
59 | the old one to serve two purposes, since it may become harder to use and | |
60 | maintain. Instead, copy and rename an existing major mode definition | |
61 | and alter the copy---or define a @dfn{derived mode} (@pxref{Derived | |
62 | Modes}). For example, Rmail Edit mode, which is in | |
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63 | @file{emacs/lisp/mail/rmailedit.el}, is a major mode that is very similar to |
64 | Text mode except that it provides two additional commands. Its | |
65 | definition is distinct from that of Text mode, but uses that of Text mode. | |
a44af9f2 | 66 | |
5858d11f | 67 | Even if the new mode is not an obvious derivative of any other mode, |
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68 | it is convenient to use @code{define-derived-mode} with a @code{nil} |
69 | parent argument, since it automatically enforces the most important | |
70 | coding conventions for you. | |
5858d11f | 71 | |
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72 | @findex define-generic-mode |
73 | For a very simple programming language major mode that handles | |
74 | comments and fontification, you can use @code{define-generic-mode} | |
75 | in @file{generic.el}. | |
76 | ||
969fe9b5 RS |
77 | Rmail Edit mode offers an example of changing the major mode |
78 | temporarily for a buffer, so it can be edited in a different way (with | |
1911e6e5 | 79 | ordinary Emacs commands rather than Rmail commands). In such cases, the |
8241495d | 80 | temporary major mode usually provides a command to switch back to the |
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81 | buffer's usual mode (Rmail mode, in this case). You might be tempted to |
82 | present the temporary redefinitions inside a recursive edit and restore | |
83 | the usual ones when the user exits; but this is a bad idea because it | |
84 | constrains the user's options when it is done in more than one buffer: | |
85 | recursive edits must be exited most-recently-entered first. Using an | |
86 | alternative major mode avoids this limitation. @xref{Recursive | |
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87 | Editing}. |
88 | ||
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89 | The standard GNU Emacs Lisp library directory tree contains the code |
90 | for several major modes, in files such as @file{text-mode.el}, | |
a44af9f2 | 91 | @file{texinfo.el}, @file{lisp-mode.el}, @file{c-mode.el}, and |
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92 | @file{rmail.el}. They are found in various subdirectories of the |
93 | @file{lisp} directory. You can study these libraries to see how modes | |
94 | are written. Text mode is perhaps the simplest major mode aside from | |
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95 | Fundamental mode. Rmail mode is a complicated and specialized mode. |
96 | ||
97 | @menu | |
98 | * Major Mode Conventions:: Coding conventions for keymaps, etc. | |
99 | * Example Major Modes:: Text mode and Lisp modes. | |
100 | * Auto Major Mode:: How Emacs chooses the major mode automatically. | |
101 | * Mode Help:: Finding out how to use a mode. | |
177c0ea7 | 102 | * Derived Modes:: Defining a new major mode based on another major |
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103 | mode. |
104 | @end menu | |
105 | ||
106 | @node Major Mode Conventions | |
107 | @subsection Major Mode Conventions | |
108 | ||
109 | The code for existing major modes follows various coding conventions, | |
110 | including conventions for local keymap and syntax table initialization, | |
111 | global names, and hooks. Please follow these conventions when you | |
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112 | define a new major mode. |
113 | ||
114 | This list of conventions is only partial, because each major mode | |
115 | should aim for consistency in general with other Emacs major modes. | |
116 | This makes Emacs as a whole more coherent. It is impossible to list | |
117 | here all the possible points where this issue might come up; if the | |
118 | Emacs developers point out an area where your major mode deviates from | |
119 | the usual conventions, please make it compatible. | |
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120 | |
121 | @itemize @bullet | |
122 | @item | |
123 | Define a command whose name ends in @samp{-mode}, with no arguments, | |
124 | that switches to the new mode in the current buffer. This command | |
969fe9b5 RS |
125 | should set up the keymap, syntax table, and buffer-local variables in an |
126 | existing buffer, without changing the buffer's contents. | |
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127 | |
128 | @item | |
de9f0bd9 | 129 | Write a documentation string for this command that describes the |
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130 | special commands available in this mode. @kbd{C-h m} |
131 | (@code{describe-mode}) in your mode will display this string. | |
132 | ||
133 | The documentation string may include the special documentation | |
134 | substrings, @samp{\[@var{command}]}, @samp{\@{@var{keymap}@}}, and | |
86494bd5 | 135 | @samp{\<@var{keymap}>}, which enable the documentation to adapt |
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136 | automatically to the user's own key bindings. @xref{Keys in |
137 | Documentation}. | |
138 | ||
139 | @item | |
140 | The major mode command should start by calling | |
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141 | @code{kill-all-local-variables}. This is what gets rid of the |
142 | buffer-local variables of the major mode previously in effect. | |
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143 | |
144 | @item | |
145 | The major mode command should set the variable @code{major-mode} to the | |
146 | major mode command symbol. This is how @code{describe-mode} discovers | |
147 | which documentation to print. | |
148 | ||
149 | @item | |
150 | The major mode command should set the variable @code{mode-name} to the | |
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151 | ``pretty'' name of the mode, as a string. This string appears in the |
152 | mode line. | |
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153 | |
154 | @item | |
155 | @cindex functions in modes | |
156 | Since all global names are in the same name space, all the global | |
157 | variables, constants, and functions that are part of the mode should | |
158 | have names that start with the major mode name (or with an abbreviation | |
a4b12c74 | 159 | of it if the name is long). @xref{Coding Conventions}. |
a44af9f2 | 160 | |
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161 | @item |
162 | In a major mode for editing some kind of structured text, such as a | |
163 | programming language, indentation of text according to structure is | |
164 | probably useful. So the mode should set @code{indent-line-function} | |
165 | to a suitable function, and probably customize other variables | |
166 | for indentation. | |
167 | ||
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168 | @item |
169 | @cindex keymaps in modes | |
170 | The major mode should usually have its own keymap, which is used as the | |
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171 | local keymap in all buffers in that mode. The major mode command should |
172 | call @code{use-local-map} to install this local map. @xref{Active | |
173 | Keymaps}, for more information. | |
a44af9f2 | 174 | |
969fe9b5 | 175 | This keymap should be stored permanently in a global variable named |
a44af9f2 | 176 | @code{@var{modename}-mode-map}. Normally the library that defines the |
de9f0bd9 | 177 | mode sets this variable. |
a44af9f2 | 178 | |
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179 | @xref{Tips for Defining}, for advice about how to write the code to set |
180 | up the mode's keymap variable. | |
181 | ||
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182 | @item |
183 | The key sequences bound in a major mode keymap should usually start with | |
969fe9b5 | 184 | @kbd{C-c}, followed by a control character, a digit, or @kbd{@{}, |
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185 | @kbd{@}}, @kbd{<}, @kbd{>}, @kbd{:} or @kbd{;}. The other punctuation |
186 | characters are reserved for minor modes, and ordinary letters are | |
187 | reserved for users. | |
188 | ||
189 | It is reasonable for a major mode to rebind a key sequence with a | |
190 | standard meaning, if it implements a command that does ``the same job'' | |
191 | in a way that fits the major mode better. For example, a major mode for | |
192 | editing a programming language might redefine @kbd{C-M-a} to ``move to | |
193 | the beginning of a function'' in a way that works better for that | |
194 | language. | |
195 | ||
196 | Major modes such as Dired or Rmail that do not allow self-insertion of | |
197 | text can reasonably redefine letters and other printing characters as | |
198 | editing commands. Dired and Rmail both do this. | |
199 | ||
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200 | @item |
201 | Major modes must not define @key{RET} to do anything other than insert | |
202 | a newline. The command to insert a newline and then indent is | |
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203 | @kbd{C-j}. Please keep this distinction uniform for all major modes. |
204 | ||
205 | @item | |
206 | Major modes should not alter options that are primary a matter of user | |
207 | preference, such as whether Auto-Fill mode is enabled. Leave this to | |
208 | each user to decide. However, a major mode should customize other | |
209 | variables so that Auto-Fill mode will work usefully @emph{if} the user | |
210 | decides to use it. | |
c2e903c0 | 211 | |
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212 | @item |
213 | @cindex syntax tables in modes | |
214 | The mode may have its own syntax table or may share one with other | |
215 | related modes. If it has its own syntax table, it should store this in | |
de9f0bd9 | 216 | a variable named @code{@var{modename}-mode-syntax-table}. @xref{Syntax |
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217 | Tables}. |
218 | ||
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219 | @item |
220 | If the mode handles a language that has a syntax for comments, it should | |
221 | set the variables that define the comment syntax. @xref{Options for | |
222 | Comments,, Options Controlling Comments, emacs, The GNU Emacs Manual}. | |
223 | ||
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224 | @item |
225 | @cindex abbrev tables in modes | |
226 | The mode may have its own abbrev table or may share one with other | |
227 | related modes. If it has its own abbrev table, it should store this in | |
228 | a variable named @code{@var{modename}-mode-abbrev-table}. @xref{Abbrev | |
229 | Tables}. | |
230 | ||
be9345cf | 231 | @item |
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232 | The mode should specify how to do highlighting for Font Lock mode, by |
233 | setting up a buffer-local value for the variable | |
969fe9b5 | 234 | @code{font-lock-defaults} (@pxref{Font Lock Mode}). |
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235 | |
236 | @item | |
be9345cf RS |
237 | The mode should specify how Imenu should find the definitions or |
238 | sections of a buffer, by setting up a buffer-local value for the | |
239 | variable @code{imenu-generic-expression} or | |
969fe9b5 | 240 | @code{imenu-create-index-function} (@pxref{Imenu}). |
be9345cf | 241 | |
de9f0bd9 | 242 | @item |
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243 | Use @code{defvar} or @code{defcustom} to set mode-related variables, so |
244 | that they are not reinitialized if they already have a value. (Such | |
245 | reinitialization could discard customizations made by the user.) | |
de9f0bd9 | 246 | |
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247 | @item |
248 | @cindex buffer-local variables in modes | |
249 | To make a buffer-local binding for an Emacs customization variable, use | |
250 | @code{make-local-variable} in the major mode command, not | |
251 | @code{make-variable-buffer-local}. The latter function would make the | |
252 | variable local to every buffer in which it is subsequently set, which | |
253 | would affect buffers that do not use this mode. It is undesirable for a | |
254 | mode to have such global effects. @xref{Buffer-Local Variables}. | |
255 | ||
177c0ea7 | 256 | With rare exceptions, the only reasonable way to use |
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257 | @code{make-variable-buffer-local} in a Lisp package is for a variable |
258 | which is used only within that package. Using it on a variable used by | |
259 | other packages would interfere with them. | |
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260 | |
261 | @item | |
262 | @cindex mode hook | |
263 | @cindex major mode hook | |
264 | Each major mode should have a @dfn{mode hook} named | |
265 | @code{@var{modename}-mode-hook}. The major mode command should run that | |
fdba9ef4 | 266 | hook, with @code{run-mode-hooks}, as the very last thing it |
a4b12c74 | 267 | does. @xref{Hooks}. |
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268 | |
269 | @item | |
fdba9ef4 RS |
270 | The major mode command may start by calling some other major mode |
271 | command (called the @dfn{parent mode}) and then alter some of its | |
272 | settings. A mode that does this is called a @dfn{derived mode}. The | |
273 | recommended way to define one is to use @code{define-derived-mode}, | |
274 | but this is not required. Such a mode should use | |
275 | @code{delay-mode-hooks} around its entire body, including the call to | |
276 | the parent mode command and the final call to @code{run-mode-hooks}. | |
277 | (Using @code{define-derived-mode} does this automatically.) | |
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278 | |
279 | @item | |
280 | If something special should be done if the user switches a buffer from | |
f9f59935 | 281 | this mode to any other major mode, this mode can set up a buffer-local |
969fe9b5 | 282 | value for @code{change-major-mode-hook} (@pxref{Creating Buffer-Local}). |
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283 | |
284 | @item | |
285 | If this mode is appropriate only for specially-prepared text, then the | |
286 | major mode command symbol should have a property named @code{mode-class} | |
287 | with value @code{special}, put on as follows: | |
288 | ||
ace41f7d | 289 | @kindex mode-class @r{(property)} |
a44af9f2 RS |
290 | @cindex @code{special} |
291 | @example | |
292 | (put 'funny-mode 'mode-class 'special) | |
293 | @end example | |
294 | ||
295 | @noindent | |
8241495d | 296 | This tells Emacs that new buffers created while the current buffer is in |
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297 | Funny mode should not inherit Funny mode. Modes such as Dired, Rmail, |
298 | and Buffer List use this feature. | |
299 | ||
300 | @item | |
301 | If you want to make the new mode the default for files with certain | |
302 | recognizable names, add an element to @code{auto-mode-alist} to select | |
303 | the mode for those file names. If you define the mode command to | |
304 | autoload, you should add this element in the same file that calls | |
305 | @code{autoload}. Otherwise, it is sufficient to add the element in the | |
306 | file that contains the mode definition. @xref{Auto Major Mode}. | |
307 | ||
308 | @item | |
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309 | In the documentation, you should provide a sample @code{autoload} form |
310 | and an example of how to add to @code{auto-mode-alist}, that users can | |
a40d4712 | 311 | include in their init files (@pxref{Init File}). |
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312 | |
313 | @item | |
314 | @cindex mode loading | |
de9f0bd9 | 315 | The top-level forms in the file defining the mode should be written so |
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316 | that they may be evaluated more than once without adverse consequences. |
317 | Even if you never load the file more than once, someone else will. | |
318 | @end itemize | |
319 | ||
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320 | @node Example Major Modes |
321 | @subsection Major Mode Examples | |
322 | ||
323 | Text mode is perhaps the simplest mode besides Fundamental mode. | |
324 | Here are excerpts from @file{text-mode.el} that illustrate many of | |
325 | the conventions listed above: | |
326 | ||
327 | @smallexample | |
328 | @group | |
329 | ;; @r{Create mode-specific tables.} | |
177c0ea7 | 330 | (defvar text-mode-syntax-table nil |
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331 | "Syntax table used while in text mode.") |
332 | @end group | |
333 | ||
334 | @group | |
335 | (if text-mode-syntax-table | |
336 | () ; @r{Do not change the table if it is already set up.} | |
337 | (setq text-mode-syntax-table (make-syntax-table)) | |
338 | (modify-syntax-entry ?\" ". " text-mode-syntax-table) | |
339 | (modify-syntax-entry ?\\ ". " text-mode-syntax-table) | |
340 | (modify-syntax-entry ?' "w " text-mode-syntax-table)) | |
341 | @end group | |
342 | ||
343 | @group | |
344 | (defvar text-mode-abbrev-table nil | |
345 | "Abbrev table used while in text mode.") | |
346 | (define-abbrev-table 'text-mode-abbrev-table ()) | |
347 | @end group | |
348 | ||
349 | @group | |
a40d4712 PR |
350 | (defvar text-mode-map nil ; @r{Create a mode-specific keymap.} |
351 | "Keymap for Text mode. | |
352 | Many other modes, such as Mail mode, Outline mode and Indented Text mode, | |
353 | inherit all the commands defined in this map.") | |
a44af9f2 RS |
354 | |
355 | (if text-mode-map | |
356 | () ; @r{Do not change the keymap if it is already set up.} | |
357 | (setq text-mode-map (make-sparse-keymap)) | |
a40d4712 | 358 | (define-key text-mode-map "\e\t" 'ispell-complete-word) |
a9f0a989 | 359 | (define-key text-mode-map "\t" 'indent-relative) |
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360 | (define-key text-mode-map "\es" 'center-line) |
361 | (define-key text-mode-map "\eS" 'center-paragraph)) | |
362 | @end group | |
363 | @end smallexample | |
364 | ||
fdba9ef4 | 365 | This was formerly the complete major mode function definition for Text mode: |
a44af9f2 RS |
366 | |
367 | @smallexample | |
368 | @group | |
369 | (defun text-mode () | |
29b677db | 370 | "Major mode for editing text intended for humans to read... |
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371 | Special commands: \\@{text-mode-map@} |
372 | @end group | |
373 | @group | |
374 | Turning on text-mode runs the hook `text-mode-hook'." | |
375 | (interactive) | |
376 | (kill-all-local-variables) | |
969fe9b5 | 377 | (use-local-map text-mode-map) |
a44af9f2 RS |
378 | @end group |
379 | @group | |
a44af9f2 RS |
380 | (setq local-abbrev-table text-mode-abbrev-table) |
381 | (set-syntax-table text-mode-syntax-table) | |
969fe9b5 RS |
382 | @end group |
383 | @group | |
384 | (make-local-variable 'paragraph-start) | |
385 | (setq paragraph-start (concat "[ \t]*$\\|" page-delimiter)) | |
386 | (make-local-variable 'paragraph-separate) | |
387 | (setq paragraph-separate paragraph-start) | |
a40d4712 PR |
388 | (make-local-variable 'indent-line-function) |
389 | (setq indent-line-function 'indent-relative-maybe) | |
969fe9b5 RS |
390 | @end group |
391 | @group | |
392 | (setq mode-name "Text") | |
393 | (setq major-mode 'text-mode) | |
fdba9ef4 | 394 | (run-mode-hooks 'text-mode-hook)) ; @r{Finally, this permits the user to} |
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395 | ; @r{customize the mode with a hook.} |
396 | @end group | |
397 | @end smallexample | |
398 | ||
399 | @cindex @file{lisp-mode.el} | |
400 | The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp | |
401 | Interaction mode) have more features than Text mode and the code is | |
402 | correspondingly more complicated. Here are excerpts from | |
403 | @file{lisp-mode.el} that illustrate how these modes are written. | |
404 | ||
405 | @cindex syntax table example | |
406 | @smallexample | |
407 | @group | |
408 | ;; @r{Create mode-specific table variables.} | |
177c0ea7 | 409 | (defvar lisp-mode-syntax-table nil "") |
a44af9f2 RS |
410 | (defvar emacs-lisp-mode-syntax-table nil "") |
411 | (defvar lisp-mode-abbrev-table nil "") | |
412 | @end group | |
413 | ||
414 | @group | |
415 | (if (not emacs-lisp-mode-syntax-table) ; @r{Do not change the table} | |
416 | ; @r{if it is already set.} | |
417 | (let ((i 0)) | |
418 | (setq emacs-lisp-mode-syntax-table (make-syntax-table)) | |
419 | @end group | |
420 | ||
421 | @group | |
422 | ;; @r{Set syntax of chars up to 0 to class of chars that are} | |
423 | ;; @r{part of symbol names but not words.} | |
8241495d | 424 | ;; @r{(The number 0 is @code{48} in the @sc{ascii} character set.)} |
177c0ea7 | 425 | (while (< i ?0) |
a44af9f2 RS |
426 | (modify-syntax-entry i "_ " emacs-lisp-mode-syntax-table) |
427 | (setq i (1+ i))) | |
428 | @dots{} | |
429 | @end group | |
430 | @group | |
431 | ;; @r{Set the syntax for other characters.} | |
432 | (modify-syntax-entry ? " " emacs-lisp-mode-syntax-table) | |
433 | (modify-syntax-entry ?\t " " emacs-lisp-mode-syntax-table) | |
434 | @dots{} | |
435 | @end group | |
436 | @group | |
437 | (modify-syntax-entry ?\( "() " emacs-lisp-mode-syntax-table) | |
438 | (modify-syntax-entry ?\) ")( " emacs-lisp-mode-syntax-table) | |
439 | @dots{})) | |
440 | ;; @r{Create an abbrev table for lisp-mode.} | |
441 | (define-abbrev-table 'lisp-mode-abbrev-table ()) | |
442 | @end group | |
443 | @end smallexample | |
444 | ||
445 | Much code is shared among the three Lisp modes. The following | |
446 | function sets various variables; it is called by each of the major Lisp | |
447 | mode functions: | |
448 | ||
449 | @smallexample | |
450 | @group | |
451 | (defun lisp-mode-variables (lisp-syntax) | |
a44af9f2 | 452 | (cond (lisp-syntax |
969fe9b5 | 453 | (set-syntax-table lisp-mode-syntax-table))) |
a44af9f2 | 454 | (setq local-abbrev-table lisp-mode-abbrev-table) |
a9f0a989 | 455 | @dots{} |
a44af9f2 RS |
456 | @end group |
457 | @end smallexample | |
458 | ||
459 | Functions such as @code{forward-paragraph} use the value of the | |
460 | @code{paragraph-start} variable. Since Lisp code is different from | |
461 | ordinary text, the @code{paragraph-start} variable needs to be set | |
462 | specially to handle Lisp. Also, comments are indented in a special | |
463 | fashion in Lisp and the Lisp modes need their own mode-specific | |
464 | @code{comment-indent-function}. The code to set these variables is the | |
465 | rest of @code{lisp-mode-variables}. | |
466 | ||
467 | @smallexample | |
468 | @group | |
469 | (make-local-variable 'paragraph-start) | |
969fe9b5 RS |
470 | (setq paragraph-start (concat page-delimiter "\\|$" )) |
471 | (make-local-variable 'paragraph-separate) | |
472 | (setq paragraph-separate paragraph-start) | |
a44af9f2 RS |
473 | @dots{} |
474 | @end group | |
475 | @group | |
476 | (make-local-variable 'comment-indent-function) | |
477 | (setq comment-indent-function 'lisp-comment-indent)) | |
a40d4712 | 478 | @dots{} |
a44af9f2 RS |
479 | @end group |
480 | @end smallexample | |
481 | ||
482 | Each of the different Lisp modes has a slightly different keymap. For | |
f9f59935 | 483 | example, Lisp mode binds @kbd{C-c C-z} to @code{run-lisp}, but the other |
a44af9f2 | 484 | Lisp modes do not. However, all Lisp modes have some commands in |
969fe9b5 | 485 | common. The following code sets up the common commands: |
a44af9f2 RS |
486 | |
487 | @smallexample | |
488 | @group | |
969fe9b5 RS |
489 | (defvar shared-lisp-mode-map () |
490 | "Keymap for commands shared by all sorts of Lisp modes.") | |
491 | ||
492 | (if shared-lisp-mode-map | |
493 | () | |
494 | (setq shared-lisp-mode-map (make-sparse-keymap)) | |
495 | (define-key shared-lisp-mode-map "\e\C-q" 'indent-sexp) | |
496 | (define-key shared-lisp-mode-map "\177" | |
497 | 'backward-delete-char-untabify)) | |
a44af9f2 RS |
498 | @end group |
499 | @end smallexample | |
500 | ||
969fe9b5 RS |
501 | @noindent |
502 | And here is the code to set up the keymap for Lisp mode: | |
a44af9f2 RS |
503 | |
504 | @smallexample | |
505 | @group | |
969fe9b5 | 506 | (defvar lisp-mode-map () |
29b677db | 507 | "Keymap for ordinary Lisp mode...") |
969fe9b5 RS |
508 | |
509 | (if lisp-mode-map | |
a44af9f2 | 510 | () |
969fe9b5 RS |
511 | (setq lisp-mode-map (make-sparse-keymap)) |
512 | (set-keymap-parent lisp-mode-map shared-lisp-mode-map) | |
513 | (define-key lisp-mode-map "\e\C-x" 'lisp-eval-defun) | |
514 | (define-key lisp-mode-map "\C-c\C-z" 'run-lisp)) | |
a44af9f2 RS |
515 | @end group |
516 | @end smallexample | |
517 | ||
518 | Finally, here is the complete major mode function definition for | |
177c0ea7 | 519 | Lisp mode. |
a44af9f2 RS |
520 | |
521 | @smallexample | |
522 | @group | |
969fe9b5 RS |
523 | (defun lisp-mode () |
524 | "Major mode for editing Lisp code for Lisps other than GNU Emacs Lisp. | |
a44af9f2 RS |
525 | Commands: |
526 | Delete converts tabs to spaces as it moves back. | |
527 | Blank lines separate paragraphs. Semicolons start comments. | |
969fe9b5 RS |
528 | \\@{lisp-mode-map@} |
529 | Note that `run-lisp' may be used either to start an inferior Lisp job | |
530 | or to switch back to an existing one. | |
a44af9f2 | 531 | @end group |
969fe9b5 | 532 | |
a44af9f2 | 533 | @group |
969fe9b5 RS |
534 | Entry to this mode calls the value of `lisp-mode-hook' |
535 | if that value is non-nil." | |
a44af9f2 RS |
536 | (interactive) |
537 | (kill-all-local-variables) | |
a44af9f2 RS |
538 | @end group |
539 | @group | |
969fe9b5 RS |
540 | (use-local-map lisp-mode-map) ; @r{Select the mode's keymap.} |
541 | (setq major-mode 'lisp-mode) ; @r{This is how @code{describe-mode}} | |
a44af9f2 | 542 | ; @r{finds out what to describe.} |
969fe9b5 RS |
543 | (setq mode-name "Lisp") ; @r{This goes into the mode line.} |
544 | (lisp-mode-variables t) ; @r{This defines various variables.} | |
545 | @end group | |
546 | @group | |
547 | (setq imenu-case-fold-search t) | |
548 | (set-syntax-table lisp-mode-syntax-table) | |
fdba9ef4 | 549 | (run-mode-hooks 'lisp-mode-hook)) ; @r{This permits the user to use a} |
a44af9f2 RS |
550 | ; @r{hook to customize the mode.} |
551 | @end group | |
552 | @end smallexample | |
553 | ||
554 | @node Auto Major Mode | |
555 | @subsection How Emacs Chooses a Major Mode | |
556 | ||
557 | Based on information in the file name or in the file itself, Emacs | |
558 | automatically selects a major mode for the new buffer when a file is | |
969fe9b5 | 559 | visited. It also processes local variables specified in the file text. |
a44af9f2 RS |
560 | |
561 | @deffn Command fundamental-mode | |
562 | Fundamental mode is a major mode that is not specialized for anything | |
563 | in particular. Other major modes are defined in effect by comparison | |
564 | with this one---their definitions say what to change, starting from | |
565 | Fundamental mode. The @code{fundamental-mode} function does @emph{not} | |
566 | run any hooks; you're not supposed to customize it. (If you want Emacs | |
567 | to behave differently in Fundamental mode, change the @emph{global} | |
568 | state of Emacs.) | |
569 | @end deffn | |
570 | ||
571 | @deffn Command normal-mode &optional find-file | |
969fe9b5 | 572 | This function establishes the proper major mode and buffer-local variable |
a44af9f2 RS |
573 | bindings for the current buffer. First it calls @code{set-auto-mode}, |
574 | then it runs @code{hack-local-variables} to parse, and bind or | |
969fe9b5 | 575 | evaluate as appropriate, the file's local variables. |
a44af9f2 | 576 | |
969fe9b5 RS |
577 | If the @var{find-file} argument to @code{normal-mode} is non-@code{nil}, |
578 | @code{normal-mode} assumes that the @code{find-file} function is calling | |
579 | it. In this case, it may process a local variables list at the end of | |
580 | the file and in the @samp{-*-} line. The variable | |
581 | @code{enable-local-variables} controls whether to do so. @xref{File | |
582 | variables, , Local Variables in Files, emacs, The GNU Emacs Manual}, for | |
583 | the syntax of the local variables section of a file. | |
a44af9f2 | 584 | |
bfe721d1 | 585 | If you run @code{normal-mode} interactively, the argument |
a44af9f2 RS |
586 | @var{find-file} is normally @code{nil}. In this case, |
587 | @code{normal-mode} unconditionally processes any local variables list. | |
a44af9f2 RS |
588 | |
589 | @cindex file mode specification error | |
bfe721d1 | 590 | @code{normal-mode} uses @code{condition-case} around the call to the |
a44af9f2 RS |
591 | major mode function, so errors are caught and reported as a @samp{File |
592 | mode specification error}, followed by the original error message. | |
593 | @end deffn | |
594 | ||
a44af9f2 RS |
595 | @defun set-auto-mode |
596 | @cindex visited file mode | |
597 | This function selects the major mode that is appropriate for the | |
598 | current buffer. It may base its decision on the value of the @w{@samp{-*-}} | |
76352dc1 RS |
599 | line, on the visited file name (using @code{auto-mode-alist}), on the |
600 | @w{@samp{#!}} line (using @code{interpreter-mode-alist}), or on the | |
969fe9b5 | 601 | file's local variables list. However, this function does not look for |
a44af9f2 RS |
602 | the @samp{mode:} local variable near the end of a file; the |
603 | @code{hack-local-variables} function does that. @xref{Choosing Modes, , | |
604 | How Major Modes are Chosen, emacs, The GNU Emacs Manual}. | |
605 | @end defun | |
606 | ||
177c0ea7 | 607 | @defopt default-major-mode |
969fe9b5 | 608 | This variable holds the default major mode for new buffers. The |
a44af9f2 RS |
609 | standard value is @code{fundamental-mode}. |
610 | ||
969fe9b5 | 611 | If the value of @code{default-major-mode} is @code{nil}, Emacs uses |
a44af9f2 | 612 | the (previously) current buffer's major mode for the major mode of a new |
f9f59935 | 613 | buffer. However, if that major mode symbol has a @code{mode-class} |
a44af9f2 RS |
614 | property with value @code{special}, then it is not used for new buffers; |
615 | Fundamental mode is used instead. The modes that have this property are | |
616 | those such as Dired and Rmail that are useful only with text that has | |
617 | been specially prepared. | |
618 | @end defopt | |
619 | ||
22697dac KH |
620 | @defun set-buffer-major-mode buffer |
621 | This function sets the major mode of @var{buffer} to the value of | |
622 | @code{default-major-mode}. If that variable is @code{nil}, it uses | |
623 | the current buffer's major mode (if that is suitable). | |
624 | ||
625 | The low-level primitives for creating buffers do not use this function, | |
bfe721d1 KH |
626 | but medium-level commands such as @code{switch-to-buffer} and |
627 | @code{find-file-noselect} use it whenever they create buffers. | |
22697dac KH |
628 | @end defun |
629 | ||
a44af9f2 RS |
630 | @defvar initial-major-mode |
631 | @cindex @samp{*scratch*} | |
632 | The value of this variable determines the major mode of the initial | |
633 | @samp{*scratch*} buffer. The value should be a symbol that is a major | |
f9f59935 | 634 | mode command. The default value is @code{lisp-interaction-mode}. |
a44af9f2 RS |
635 | @end defvar |
636 | ||
637 | @defvar auto-mode-alist | |
638 | This variable contains an association list of file name patterns | |
639 | (regular expressions; @pxref{Regular Expressions}) and corresponding | |
f9f59935 RS |
640 | major mode commands. Usually, the file name patterns test for suffixes, |
641 | such as @samp{.el} and @samp{.c}, but this need not be the case. An | |
642 | ordinary element of the alist looks like @code{(@var{regexp} . | |
a44af9f2 RS |
643 | @var{mode-function})}. |
644 | ||
645 | For example, | |
646 | ||
647 | @smallexample | |
648 | @group | |
969fe9b5 | 649 | (("\\`/tmp/fol/" . text-mode) |
24675e99 RS |
650 | ("\\.texinfo\\'" . texinfo-mode) |
651 | ("\\.texi\\'" . texinfo-mode) | |
a44af9f2 RS |
652 | @end group |
653 | @group | |
24675e99 | 654 | ("\\.el\\'" . emacs-lisp-mode) |
177c0ea7 | 655 | ("\\.c\\'" . c-mode) |
24675e99 | 656 | ("\\.h\\'" . c-mode) |
a44af9f2 RS |
657 | @dots{}) |
658 | @end group | |
659 | @end smallexample | |
660 | ||
661 | When you visit a file whose expanded file name (@pxref{File Name | |
662 | Expansion}) matches a @var{regexp}, @code{set-auto-mode} calls the | |
663 | corresponding @var{mode-function}. This feature enables Emacs to select | |
664 | the proper major mode for most files. | |
665 | ||
666 | If an element of @code{auto-mode-alist} has the form @code{(@var{regexp} | |
667 | @var{function} t)}, then after calling @var{function}, Emacs searches | |
668 | @code{auto-mode-alist} again for a match against the portion of the file | |
969fe9b5 RS |
669 | name that did not match before. This feature is useful for |
670 | uncompression packages: an entry of the form @code{("\\.gz\\'" | |
671 | @var{function} t)} can uncompress the file and then put the uncompressed | |
672 | file in the proper mode according to the name sans @samp{.gz}. | |
a44af9f2 RS |
673 | |
674 | Here is an example of how to prepend several pattern pairs to | |
675 | @code{auto-mode-alist}. (You might use this sort of expression in your | |
a40d4712 | 676 | init file.) |
a44af9f2 RS |
677 | |
678 | @smallexample | |
679 | @group | |
680 | (setq auto-mode-alist | |
177c0ea7 | 681 | (append |
f9f59935 | 682 | ;; @r{File name (within directory) starts with a dot.} |
177c0ea7 | 683 | '(("/\\.[^/]*\\'" . fundamental-mode) |
de9f0bd9 | 684 | ;; @r{File name has no dot.} |
177c0ea7 | 685 | ("[^\\./]*\\'" . fundamental-mode) |
de9f0bd9 | 686 | ;; @r{File name ends in @samp{.C}.} |
24675e99 | 687 | ("\\.C\\'" . c++-mode)) |
a44af9f2 RS |
688 | auto-mode-alist)) |
689 | @end group | |
690 | @end smallexample | |
691 | @end defvar | |
692 | ||
693 | @defvar interpreter-mode-alist | |
f9f59935 | 694 | This variable specifies major modes to use for scripts that specify a |
86494bd5 | 695 | command interpreter in a @samp{#!} line. Its value is a list of |
a44af9f2 RS |
696 | elements of the form @code{(@var{interpreter} . @var{mode})}; for |
697 | example, @code{("perl" . perl-mode)} is one element present by default. | |
698 | The element says to use mode @var{mode} if the file specifies | |
f9f59935 RS |
699 | an interpreter which matches @var{interpreter}. The value of |
700 | @var{interpreter} is actually a regular expression. | |
a44af9f2 | 701 | |
de9f0bd9 RS |
702 | This variable is applicable only when the @code{auto-mode-alist} does |
703 | not indicate which major mode to use. | |
a44af9f2 RS |
704 | @end defvar |
705 | ||
a44af9f2 RS |
706 | @node Mode Help |
707 | @subsection Getting Help about a Major Mode | |
708 | @cindex mode help | |
709 | @cindex help for major mode | |
710 | @cindex documentation for major mode | |
711 | ||
712 | The @code{describe-mode} function is used to provide information | |
713 | about major modes. It is normally called with @kbd{C-h m}. The | |
714 | @code{describe-mode} function uses the value of @code{major-mode}, | |
715 | which is why every major mode function needs to set the | |
716 | @code{major-mode} variable. | |
717 | ||
718 | @deffn Command describe-mode | |
719 | This function displays the documentation of the current major mode. | |
720 | ||
721 | The @code{describe-mode} function calls the @code{documentation} | |
722 | function using the value of @code{major-mode} as an argument. Thus, it | |
723 | displays the documentation string of the major mode function. | |
724 | (@xref{Accessing Documentation}.) | |
725 | @end deffn | |
726 | ||
727 | @defvar major-mode | |
728 | This variable holds the symbol for the current buffer's major mode. | |
de9f0bd9 | 729 | This symbol should have a function definition that is the command to |
a44af9f2 | 730 | switch to that major mode. The @code{describe-mode} function uses the |
de9f0bd9 | 731 | documentation string of the function as the documentation of the major |
a44af9f2 RS |
732 | mode. |
733 | @end defvar | |
734 | ||
735 | @node Derived Modes | |
736 | @subsection Defining Derived Modes | |
737 | ||
738 | It's often useful to define a new major mode in terms of an existing | |
739 | one. An easy way to do this is to use @code{define-derived-mode}. | |
740 | ||
de9f0bd9 | 741 | @defmac define-derived-mode variant parent name docstring body@dots{} |
a44af9f2 | 742 | This construct defines @var{variant} as a major mode command, using |
de9f0bd9 | 743 | @var{name} as the string form of the mode name. |
a44af9f2 | 744 | |
de9f0bd9 RS |
745 | The new command @var{variant} is defined to call the function |
746 | @var{parent}, then override certain aspects of that parent mode: | |
a44af9f2 | 747 | |
177c0ea7 | 748 | @itemize @bullet |
a44af9f2 RS |
749 | @item |
750 | The new mode has its own keymap, named @code{@var{variant}-map}. | |
751 | @code{define-derived-mode} initializes this map to inherit from | |
752 | @code{@var{parent}-map}, if it is not already set. | |
753 | ||
754 | @item | |
de9f0bd9 | 755 | The new mode has its own syntax table, kept in the variable |
a44af9f2 | 756 | @code{@var{variant}-syntax-table}. |
177c0ea7 | 757 | @code{define-derived-mode} initializes this variable by copying |
a44af9f2 RS |
758 | @code{@var{parent}-syntax-table}, if it is not already set. |
759 | ||
760 | @item | |
de9f0bd9 | 761 | The new mode has its own abbrev table, kept in the variable |
a44af9f2 | 762 | @code{@var{variant}-abbrev-table}. |
177c0ea7 | 763 | @code{define-derived-mode} initializes this variable by copying |
a44af9f2 RS |
764 | @code{@var{parent}-abbrev-table}, if it is not already set. |
765 | ||
766 | @item | |
767 | The new mode has its own mode hook, @code{@var{variant}-hook}, | |
768 | which it runs in standard fashion as the very last thing that it does. | |
177c0ea7 | 769 | (The new mode also runs the mode hook of @var{parent} as part |
a44af9f2 RS |
770 | of calling @var{parent}.) |
771 | @end itemize | |
772 | ||
773 | In addition, you can specify how to override other aspects of | |
de9f0bd9 | 774 | @var{parent} with @var{body}. The command @var{variant} |
177c0ea7 | 775 | evaluates the forms in @var{body} after setting up all its usual |
a44af9f2 RS |
776 | overrides, just before running @code{@var{variant}-hook}. |
777 | ||
778 | The argument @var{docstring} specifies the documentation string for the | |
779 | new mode. If you omit @var{docstring}, @code{define-derived-mode} | |
780 | generates a documentation string. | |
781 | ||
782 | Here is a hypothetical example: | |
783 | ||
784 | @example | |
785 | (define-derived-mode hypertext-mode | |
786 | text-mode "Hypertext" | |
787 | "Major mode for hypertext. | |
788 | \\@{hypertext-mode-map@}" | |
789 | (setq case-fold-search nil)) | |
790 | ||
791 | (define-key hypertext-mode-map | |
792 | [down-mouse-3] 'do-hyper-link) | |
793 | @end example | |
f140458b RS |
794 | |
795 | Do not write an @code{interactive} spec in the definition; | |
796 | @code{define-derived-mode} does that automatically. | |
a44af9f2 RS |
797 | @end defmac |
798 | ||
799 | @node Minor Modes | |
800 | @section Minor Modes | |
801 | @cindex minor mode | |
802 | ||
803 | A @dfn{minor mode} provides features that users may enable or disable | |
804 | independently of the choice of major mode. Minor modes can be enabled | |
805 | individually or in combination. Minor modes would be better named | |
969fe9b5 RS |
806 | ``generally available, optional feature modes,'' except that such a name |
807 | would be unwieldy. | |
a44af9f2 | 808 | |
8241495d RS |
809 | A minor mode is not usually meant as a variation of a single major mode. |
810 | Usually they are general and can apply to many major modes. For | |
969fe9b5 | 811 | example, Auto Fill mode works with any major mode that permits text |
a44af9f2 RS |
812 | insertion. To be general, a minor mode must be effectively independent |
813 | of the things major modes do. | |
814 | ||
815 | A minor mode is often much more difficult to implement than a major | |
816 | mode. One reason is that you should be able to activate and deactivate | |
de9f0bd9 RS |
817 | minor modes in any order. A minor mode should be able to have its |
818 | desired effect regardless of the major mode and regardless of the other | |
819 | minor modes in effect. | |
a44af9f2 RS |
820 | |
821 | Often the biggest problem in implementing a minor mode is finding a | |
822 | way to insert the necessary hook into the rest of Emacs. Minor mode | |
bfe721d1 | 823 | keymaps make this easier than it used to be. |
a44af9f2 | 824 | |
fdba9ef4 RS |
825 | @defvar minor-mode-list |
826 | The value of this variable is a list of all minor mode commands. | |
827 | @end defvar | |
828 | ||
a44af9f2 RS |
829 | @menu |
830 | * Minor Mode Conventions:: Tips for writing a minor mode. | |
831 | * Keymaps and Minor Modes:: How a minor mode can have its own keymap. | |
2468d0c0 | 832 | * Defining Minor Modes:: A convenient facility for defining minor modes. |
a44af9f2 RS |
833 | @end menu |
834 | ||
835 | @node Minor Mode Conventions | |
836 | @subsection Conventions for Writing Minor Modes | |
837 | @cindex minor mode conventions | |
838 | @cindex conventions for writing minor modes | |
839 | ||
840 | There are conventions for writing minor modes just as there are for | |
841 | major modes. Several of the major mode conventions apply to minor | |
842 | modes as well: those regarding the name of the mode initialization | |
843 | function, the names of global symbols, and the use of keymaps and | |
844 | other tables. | |
845 | ||
846 | In addition, there are several conventions that are specific to | |
847 | minor modes. | |
848 | ||
849 | @itemize @bullet | |
850 | @item | |
851 | @cindex mode variable | |
969fe9b5 RS |
852 | Make a variable whose name ends in @samp{-mode} to control the minor |
853 | mode. We call this the @dfn{mode variable}. The minor mode command | |
854 | should set this variable (@code{nil} to disable; anything else to | |
1911e6e5 | 855 | enable). |
969fe9b5 | 856 | |
8241495d | 857 | If possible, implement the mode so that setting the variable |
969fe9b5 | 858 | automatically enables or disables the mode. Then the minor mode command |
1911e6e5 | 859 | does not need to do anything except set the variable. |
a44af9f2 RS |
860 | |
861 | This variable is used in conjunction with the @code{minor-mode-alist} to | |
862 | display the minor mode name in the mode line. It can also enable | |
863 | or disable a minor mode keymap. Individual commands or hooks can also | |
864 | check the variable's value. | |
865 | ||
866 | If you want the minor mode to be enabled separately in each buffer, | |
867 | make the variable buffer-local. | |
868 | ||
869 | @item | |
870 | Define a command whose name is the same as the mode variable. | |
871 | Its job is to enable and disable the mode by setting the variable. | |
872 | ||
873 | The command should accept one optional argument. If the argument is | |
8cd4f018 RS |
874 | @code{nil}, it should toggle the mode (turn it on if it is off, and |
875 | off if it is on). It should turn the mode on if the argument is a | |
876 | positive integer, the symbol @code{t}, or a list whose @sc{car} is one | |
877 | of those. It should turn the mode off if the argument is a negative | |
878 | integer or zero, the symbol @code{-}, or a list whose @sc{car} is one | |
879 | of those. The meaning of other arguments is not specified. | |
a44af9f2 | 880 | |
bfe721d1 KH |
881 | Here is an example taken from the definition of @code{transient-mark-mode}. |
882 | It shows the use of @code{transient-mark-mode} as a variable that enables or | |
de9f0bd9 RS |
883 | disables the mode's behavior, and also shows the proper way to toggle, |
884 | enable or disable the minor mode based on the raw prefix argument value. | |
a44af9f2 RS |
885 | |
886 | @smallexample | |
887 | @group | |
bfe721d1 KH |
888 | (setq transient-mark-mode |
889 | (if (null arg) (not transient-mark-mode) | |
a44af9f2 RS |
890 | (> (prefix-numeric-value arg) 0))) |
891 | @end group | |
892 | @end smallexample | |
893 | ||
894 | @item | |
895 | Add an element to @code{minor-mode-alist} for each minor mode | |
969fe9b5 RS |
896 | (@pxref{Mode Line Variables}), if you want to indicate the minor mode in |
897 | the mode line. This element should be a list of the following form: | |
a44af9f2 RS |
898 | |
899 | @smallexample | |
900 | (@var{mode-variable} @var{string}) | |
901 | @end smallexample | |
902 | ||
de9f0bd9 | 903 | Here @var{mode-variable} is the variable that controls enabling of the |
a44af9f2 RS |
904 | minor mode, and @var{string} is a short string, starting with a space, |
905 | to represent the mode in the mode line. These strings must be short so | |
906 | that there is room for several of them at once. | |
907 | ||
908 | When you add an element to @code{minor-mode-alist}, use @code{assq} to | |
909 | check for an existing element, to avoid duplication. For example: | |
910 | ||
911 | @smallexample | |
912 | @group | |
a40d4712 PR |
913 | (unless (assq 'leif-mode minor-mode-alist) |
914 | (setq minor-mode-alist | |
915 | (cons '(leif-mode " Leif") minor-mode-alist))) | |
a44af9f2 RS |
916 | @end group |
917 | @end smallexample | |
a44af9f2 | 918 | |
a40d4712 PR |
919 | @noindent |
920 | or like this, using @code{add-to-list} (@pxref{Setting Variables}): | |
921 | ||
922 | @smallexample | |
923 | @group | |
924 | (add-to-list 'minor-mode-alist '(leif-mode " Leif")) | |
925 | @end group | |
926 | @end smallexample | |
927 | @end itemize | |
1911e6e5 | 928 | |
8241495d RS |
929 | Global minor modes distributed with Emacs should if possible support |
930 | enabling and disabling via Custom (@pxref{Customization}). To do this, | |
931 | the first step is to define the mode variable with @code{defcustom}, and | |
932 | specify @code{:type boolean}. | |
933 | ||
934 | If just setting the variable is not sufficient to enable the mode, you | |
935 | should also specify a @code{:set} method which enables the mode by | |
936 | invoke the mode command. Note in the variable's documentation string that | |
937 | setting the variable other than via Custom may not take effect. | |
938 | ||
939 | Also mark the definition with an autoload cookie (@pxref{Autoload}), | |
940 | and specify a @code{:require} so that customizing the variable will load | |
941 | the library that defines the mode. This will copy suitable definitions | |
942 | into @file{loaddefs.el} so that users can use @code{customize-option} to | |
943 | enable the mode. For example: | |
944 | ||
945 | @smallexample | |
946 | @group | |
947 | ||
948 | ;;;###autoload | |
949 | (defcustom msb-mode nil | |
950 | "Toggle msb-mode. | |
951 | Setting this variable directly does not take effect; | |
952 | use either \\[customize] or the function `msb-mode'." | |
953 | :set (lambda (symbol value) | |
954 | (msb-mode (or value 0))) | |
955 | :initialize 'custom-initialize-default | |
956 | :version "20.4" | |
957 | :type 'boolean | |
958 | :group 'msb | |
959 | :require 'msb) | |
960 | @end group | |
961 | @end smallexample | |
962 | ||
a44af9f2 RS |
963 | @node Keymaps and Minor Modes |
964 | @subsection Keymaps and Minor Modes | |
965 | ||
bfe721d1 KH |
966 | Each minor mode can have its own keymap, which is active when the mode |
967 | is enabled. To set up a keymap for a minor mode, add an element to the | |
968 | alist @code{minor-mode-map-alist}. @xref{Active Keymaps}. | |
a44af9f2 RS |
969 | |
970 | @cindex @code{self-insert-command}, minor modes | |
f9f59935 | 971 | One use of minor mode keymaps is to modify the behavior of certain |
a44af9f2 RS |
972 | self-inserting characters so that they do something else as well as |
973 | self-insert. In general, this is the only way to do that, since the | |
974 | facilities for customizing @code{self-insert-command} are limited to | |
975 | special cases (designed for abbrevs and Auto Fill mode). (Do not try | |
976 | substituting your own definition of @code{self-insert-command} for the | |
977 | standard one. The editor command loop handles this function specially.) | |
978 | ||
a4b12c74 RS |
979 | The key sequences bound in a minor mode should consist of @kbd{C-c} |
980 | followed by a punctuation character @emph{other than} @kbd{@{}, | |
8241495d | 981 | @kbd{@}}, @kbd{<}, @kbd{>}, @kbd{:}, and @kbd{;}. (Those few punctuation |
a4b12c74 RS |
982 | characters are reserved for major modes.) |
983 | ||
2468d0c0 DL |
984 | @node Defining Minor Modes |
985 | @subsection Defining Minor Modes | |
f9f59935 | 986 | |
2468d0c0 DL |
987 | The macro @code{define-minor-mode} offers a convenient way of |
988 | implementing a mode in one self-contained definition. It supports only | |
8241495d | 989 | buffer-local minor modes, not global ones. |
f9f59935 | 990 | |
fdba9ef4 | 991 | @defmac define-minor-mode mode doc [init-value [lighter [keymap keyword-args... body...]]] |
2468d0c0 | 992 | @tindex define-minor-mode |
fdba9ef4 RS |
993 | This macro defines a new minor mode whose name is @var{mode} (a |
994 | symbol). It defines a command named @var{mode} to toggle the minor | |
2468d0c0 DL |
995 | mode, with @var{doc} as its documentation string. It also defines a |
996 | variable named @var{mode}, which is set to @code{t} or @code{nil} by | |
997 | enabling or disabling the mode. The variable is initialized to | |
998 | @var{init-value}. | |
f9f59935 | 999 | |
fdba9ef4 | 1000 | The string @var{lighter} says what to display in the mode line |
f9f59935 RS |
1001 | when the mode is enabled; if it is @code{nil}, the mode is not displayed |
1002 | in the mode line. | |
1003 | ||
1004 | The optional argument @var{keymap} specifies the keymap for the minor mode. | |
1005 | It can be a variable name, whose value is the keymap, or it can be an alist | |
1006 | specifying bindings in this form: | |
1007 | ||
1008 | @example | |
1009 | (@var{key-sequence} . @var{definition}) | |
1010 | @end example | |
fdba9ef4 RS |
1011 | |
1012 | The @var{keyword-args} consist of keywords followed by corresponding | |
1013 | values. A few keywords have special meanings: | |
1014 | ||
1015 | @table @code | |
1016 | @item :global @var{global} | |
1017 | If non-@code{nil} specifies that the minor mode should be global. | |
1018 | By default, minor modes are buffer-local. | |
1019 | ||
1020 | @item :init-value @var{init-value} | |
1021 | This is equivalent to specifying @var{init-value} positionally. | |
1022 | ||
1023 | @item :lighter @var{lighter} | |
1024 | This is equivalent to specifying @var{lighter} positionally. | |
1025 | ||
1026 | @item :keymap @var{keymap} | |
1027 | This is equivalent to specifying @var{keymap} positionally. | |
1028 | @end table | |
1029 | ||
1030 | Any other keyword arguments are passed passed directly to the | |
1031 | @code{defcustom} generated for the variable @var{mode}. | |
1032 | ||
1033 | The command named @var{mode} finishes by executing the @var{body} forms, | |
1034 | if any, after it has performed the standard actions such as setting | |
1035 | the variable named @var{mode}. | |
f9f59935 RS |
1036 | @end defmac |
1037 | ||
fdba9ef4 RS |
1038 | @findex easy-mmode-define-minor-mode |
1039 | The name @code{easy-mmode-define-minor-mode} is an alias | |
1040 | for this macro. | |
1041 | ||
2468d0c0 | 1042 | Here is an example of using @code{define-minor-mode}: |
f9f59935 RS |
1043 | |
1044 | @smallexample | |
2468d0c0 | 1045 | (define-minor-mode hungry-mode |
969fe9b5 | 1046 | "Toggle Hungry mode. |
177c0ea7 | 1047 | With no argument, this command toggles the mode. |
f9f59935 RS |
1048 | Non-null prefix argument turns on the mode. |
1049 | Null prefix argument turns off the mode. | |
1050 | ||
1051 | When Hungry mode is enabled, the control delete key | |
1052 | gobbles all preceding whitespace except the last. | |
1053 | See the command \\[hungry-electric-delete]." | |
1054 | ;; The initial value. | |
1055 | nil | |
1056 | ;; The indicator for the mode line. | |
1057 | " Hungry" | |
1058 | ;; The minor mode bindings. | |
1059 | '(("\C-\^?" . hungry-electric-delete) | |
1060 | ("\C-\M-\^?" | |
177c0ea7 | 1061 | . (lambda () |
f9f59935 | 1062 | (interactive) |
fdba9ef4 RS |
1063 | (hungry-electric-delete t)))) |
1064 | :group 'hunger) | |
f9f59935 RS |
1065 | @end smallexample |
1066 | ||
1067 | @noindent | |
1068 | This defines a minor mode named ``Hungry mode'', a command named | |
1069 | @code{hungry-mode} to toggle it, a variable named @code{hungry-mode} | |
1070 | which indicates whether the mode is enabled, and a variable named | |
1071 | @code{hungry-mode-map} which holds the keymap that is active when the | |
1072 | mode is enabled. It initializes the keymap with key bindings for | |
fdba9ef4 RS |
1073 | @kbd{C-@key{DEL}} and @kbd{C-M-@key{DEL}}. It puts the variable |
1074 | @code{hungry-mode} into custom group @code{hunger}. There are no | |
1075 | @var{body} forms---many minor modes don't need any. | |
f9f59935 | 1076 | |
fdba9ef4 | 1077 | Here's an equivalent way to write it: |
2468d0c0 | 1078 | |
fdba9ef4 RS |
1079 | @smallexample |
1080 | (define-minor-mode hungry-mode | |
1081 | "Toggle Hungry mode. | |
1082 | With no argument, this command toggles the mode. | |
1083 | Non-null prefix argument turns on the mode. | |
1084 | Null prefix argument turns off the mode. | |
1085 | ||
1086 | When Hungry mode is enabled, the control delete key | |
1087 | gobbles all preceding whitespace except the last. | |
1088 | See the command \\[hungry-electric-delete]." | |
1089 | ;; The initial value. | |
1090 | :initial-value nil | |
1091 | ;; The indicator for the mode line. | |
1092 | :lighter " Hungry" | |
1093 | ;; The minor mode bindings. | |
1094 | :keymap | |
1095 | '(("\C-\^?" . hungry-electric-delete) | |
1096 | ("\C-\M-\^?" | |
1097 | . (lambda () | |
1098 | (interactive) | |
1099 | (hungry-electric-delete t)))) | |
1100 | :group 'hunger) | |
1101 | @end smallexample | |
2468d0c0 | 1102 | |
a44af9f2 RS |
1103 | @node Mode Line Format |
1104 | @section Mode Line Format | |
1105 | @cindex mode line | |
1106 | ||
8241495d RS |
1107 | Each Emacs window (aside from minibuffer windows) typically has a mode |
1108 | line at the bottom, which displays status information about the buffer | |
1109 | displayed in the window. The mode line contains information about the | |
1110 | buffer, such as its name, associated file, depth of recursive editing, | |
1111 | and major and minor modes. A window can also have a @dfn{header | |
1112 | line}, which is much like the mode line but appears at the top of the | |
1113 | window (starting in Emacs 21). | |
a44af9f2 | 1114 | |
8241495d RS |
1115 | This section describes how to control the contents of the mode line |
1116 | and header line. We include it in this chapter because much of the | |
a44af9f2 RS |
1117 | information displayed in the mode line relates to the enabled major and |
1118 | minor modes. | |
1119 | ||
1120 | @code{mode-line-format} is a buffer-local variable that holds a | |
1121 | template used to display the mode line of the current buffer. All | |
8241495d RS |
1122 | windows for the same buffer use the same @code{mode-line-format}, so |
1123 | their mode lines appear the same---except for scrolling percentages, and | |
1124 | line and column numbers, since those depend on point and on how the | |
1125 | window is scrolled. @code{header-line-format} is used likewise for | |
1126 | header lines. | |
1127 | ||
8e0f7b5b RS |
1128 | For efficiency, Emacs does not recompute the mode line and header |
1129 | line of a window in every redisplay. It does so when circumstances | |
1130 | appear to call for it---for instance, if you change the window | |
1131 | configuration, switch buffers, narrow or widen the buffer, scroll, or | |
1132 | change the buffer's modification status. If you modify any of the | |
1133 | variables referenced by @code{mode-line-format} (@pxref{Mode Line | |
1134 | Variables}), or any other variables and data structures that affect | |
1135 | how text is displayed (@pxref{Display}), you may want to force an | |
1136 | update of the mode line so as to display the new information or | |
1137 | display it in the new way. | |
a44af9f2 RS |
1138 | |
1139 | @c Emacs 19 feature | |
1140 | @defun force-mode-line-update | |
8241495d | 1141 | Force redisplay of the current buffer's mode line and header line. |
8e0f7b5b RS |
1142 | The next redisplay will update the mode line and header line based on |
1143 | the latest values of all relevant variables. | |
1144 | ||
1145 | This function also forces recomputation of the menu bar menus | |
1146 | and the frame title. | |
a44af9f2 RS |
1147 | @end defun |
1148 | ||
1149 | The mode line is usually displayed in inverse video; see | |
1150 | @code{mode-line-inverse-video} in @ref{Inverse Video}. | |
1151 | ||
a1112b37 RS |
1152 | A window that is just one line tall does not display either a mode |
1153 | line or a header line, even if the variables call for one. A window | |
1154 | that is two lines tall cannot display both a mode line and a header | |
1155 | line at once; if the variables call for both, only the mode line | |
1156 | actually appears. | |
1157 | ||
a44af9f2 RS |
1158 | @menu |
1159 | * Mode Line Data:: The data structure that controls the mode line. | |
1160 | * Mode Line Variables:: Variables used in that data structure. | |
1161 | * %-Constructs:: Putting information into a mode line. | |
8241495d RS |
1162 | * Properties in Mode:: Using text properties in the mode line. |
1163 | * Header Lines:: Like a mode line, but at the top. | |
3ebe0346 | 1164 | * Emulating Mode Line:: Formatting text as the mode line would. |
a44af9f2 RS |
1165 | @end menu |
1166 | ||
1167 | @node Mode Line Data | |
1168 | @subsection The Data Structure of the Mode Line | |
1169 | @cindex mode line construct | |
1170 | ||
1171 | The mode line contents are controlled by a data structure of lists, | |
a40d4712 PR |
1172 | strings, symbols, and numbers kept in buffer-local variables. The data |
1173 | structure is called a @dfn{mode line construct}, and it is built in | |
1174 | recursive fashion out of simpler mode line constructs. The same data | |
1175 | structure is used for constructing frame titles (@pxref{Frame Titles}) | |
1176 | and header lines (@pxref{Header Lines}). | |
a44af9f2 RS |
1177 | |
1178 | @defvar mode-line-format | |
1179 | The value of this variable is a mode line construct with overall | |
1180 | responsibility for the mode line format. The value of this variable | |
1181 | controls which other variables are used to form the mode line text, and | |
1182 | where they appear. | |
8241495d RS |
1183 | |
1184 | If you set this variable to @code{nil} in a buffer, that buffer does not | |
1185 | have a mode line. (This feature was added in Emacs 21.) | |
a44af9f2 RS |
1186 | @end defvar |
1187 | ||
1188 | A mode line construct may be as simple as a fixed string of text, but | |
1189 | it usually specifies how to use other variables to construct the text. | |
1190 | Many of these variables are themselves defined to have mode line | |
1191 | constructs as their values. | |
1192 | ||
1193 | The default value of @code{mode-line-format} incorporates the values | |
1194 | of variables such as @code{mode-name} and @code{minor-mode-alist}. | |
f9f59935 RS |
1195 | Because of this, very few modes need to alter @code{mode-line-format} |
1196 | itself. For most purposes, it is sufficient to alter some of the | |
1197 | variables that @code{mode-line-format} refers to. | |
a44af9f2 | 1198 | |
de9f0bd9 RS |
1199 | A mode line construct may be a list, a symbol, or a string. If the |
1200 | value is a list, each element may be a list, a symbol, or a string. | |
a44af9f2 | 1201 | |
8241495d RS |
1202 | The mode line can display various faces, if the strings that control |
1203 | it have the @code{face} property. @xref{Properties in Mode}. In | |
1204 | addition, the face @code{mode-line} is used as a default for the whole | |
1205 | mode line (@pxref{Standard Faces}). | |
1206 | ||
a44af9f2 RS |
1207 | @table @code |
1208 | @cindex percent symbol in mode line | |
1209 | @item @var{string} | |
1210 | A string as a mode line construct is displayed verbatim in the mode line | |
bfe721d1 | 1211 | except for @dfn{@code{%}-constructs}. Decimal digits after the @samp{%} |
a44af9f2 RS |
1212 | specify the field width for space filling on the right (i.e., the data |
1213 | is left justified). @xref{%-Constructs}. | |
1214 | ||
1215 | @item @var{symbol} | |
1216 | A symbol as a mode line construct stands for its value. The value of | |
de9f0bd9 | 1217 | @var{symbol} is used as a mode line construct, in place of @var{symbol}. |
8241495d | 1218 | However, the symbols @code{t} and @code{nil} are ignored, as is any |
de9f0bd9 | 1219 | symbol whose value is void. |
a44af9f2 RS |
1220 | |
1221 | There is one exception: if the value of @var{symbol} is a string, it is | |
de9f0bd9 | 1222 | displayed verbatim: the @code{%}-constructs are not recognized. |
a44af9f2 RS |
1223 | |
1224 | @item (@var{string} @var{rest}@dots{}) @r{or} (@var{list} @var{rest}@dots{}) | |
de9f0bd9 RS |
1225 | A list whose first element is a string or list means to process all the |
1226 | elements recursively and concatenate the results. This is the most | |
1227 | common form of mode line construct. | |
a44af9f2 | 1228 | |
8241495d RS |
1229 | @item (:eval @var{form}) |
1230 | A list whose first element is the symbol @code{:eval} says to evaluate | |
1231 | @var{form}, and use the result as a string to display. | |
1232 | (This feature is new as of Emacs 21.) | |
1233 | ||
a44af9f2 | 1234 | @item (@var{symbol} @var{then} @var{else}) |
8241495d RS |
1235 | A list whose first element is a symbol that is not a keyword specifies a |
1236 | conditional. Its meaning depends on the value of @var{symbol}. If the | |
1237 | value is non-@code{nil}, the second element, @var{then}, is processed | |
1238 | recursively as a mode line element. But if the value of @var{symbol} is | |
1239 | @code{nil}, the third element, @var{else}, is processed recursively. | |
1240 | You may omit @var{else}; then the mode line element displays nothing if | |
1241 | the value of @var{symbol} is @code{nil}. | |
a44af9f2 RS |
1242 | |
1243 | @item (@var{width} @var{rest}@dots{}) | |
1244 | A list whose first element is an integer specifies truncation or | |
1245 | padding of the results of @var{rest}. The remaining elements | |
1246 | @var{rest} are processed recursively as mode line constructs and | |
1247 | concatenated together. Then the result is space filled (if | |
1248 | @var{width} is positive) or truncated (to @minus{}@var{width} columns, | |
1249 | if @var{width} is negative) on the right. | |
1250 | ||
1251 | For example, the usual way to show what percentage of a buffer is above | |
de9f0bd9 | 1252 | the top of the window is to use a list like this: @code{(-3 "%p")}. |
a44af9f2 RS |
1253 | @end table |
1254 | ||
1255 | If you do alter @code{mode-line-format} itself, the new value should | |
de9f0bd9 RS |
1256 | use the same variables that appear in the default value (@pxref{Mode |
1257 | Line Variables}), rather than duplicating their contents or displaying | |
1258 | the information in another fashion. This way, customizations made by | |
bfe721d1 KH |
1259 | the user or by Lisp programs (such as @code{display-time} and major |
1260 | modes) via changes to those variables remain effective. | |
a44af9f2 RS |
1261 | |
1262 | @cindex Shell mode @code{mode-line-format} | |
1263 | Here is an example of a @code{mode-line-format} that might be | |
969fe9b5 | 1264 | useful for @code{shell-mode}, since it contains the host name and default |
a44af9f2 RS |
1265 | directory. |
1266 | ||
1267 | @example | |
1268 | @group | |
1269 | (setq mode-line-format | |
969fe9b5 RS |
1270 | (list "-" |
1271 | 'mode-line-mule-info | |
a44af9f2 | 1272 | 'mode-line-modified |
969fe9b5 | 1273 | 'mode-line-frame-identification |
177c0ea7 | 1274 | "%b--" |
a44af9f2 | 1275 | @end group |
f9f59935 RS |
1276 | @group |
1277 | ;; @r{Note that this is evaluated while making the list.} | |
1278 | ;; @r{It makes a mode line construct which is just a string.} | |
1279 | (getenv "HOST") | |
1280 | @end group | |
177c0ea7 | 1281 | ":" |
a44af9f2 RS |
1282 | 'default-directory |
1283 | " " | |
1284 | 'global-mode-string | |
de9f0bd9 | 1285 | " %[(" |
8241495d | 1286 | '(:eval (mode-line-mode-name)) |
177c0ea7 JB |
1287 | 'mode-line-process |
1288 | 'minor-mode-alist | |
1289 | "%n" | |
969fe9b5 | 1290 | ")%]--" |
a44af9f2 | 1291 | @group |
969fe9b5 | 1292 | '(which-func-mode ("" which-func-format "--")) |
bfe721d1 | 1293 | '(line-number-mode "L%l--") |
969fe9b5 | 1294 | '(column-number-mode "C%c--") |
a44af9f2 RS |
1295 | '(-3 . "%p") |
1296 | "-%-")) | |
1297 | @end group | |
1298 | @end example | |
1299 | ||
1911e6e5 RS |
1300 | @noindent |
1301 | (The variables @code{line-number-mode}, @code{column-number-mode} | |
1302 | and @code{which-func-mode} enable particular minor modes; as usual, | |
1303 | these variable names are also the minor mode command names.) | |
1304 | ||
a44af9f2 RS |
1305 | @node Mode Line Variables |
1306 | @subsection Variables Used in the Mode Line | |
1307 | ||
1308 | This section describes variables incorporated by the | |
1309 | standard value of @code{mode-line-format} into the text of the mode | |
1310 | line. There is nothing inherently special about these variables; any | |
1311 | other variables could have the same effects on the mode line if | |
1312 | @code{mode-line-format} were changed to use them. | |
1313 | ||
969fe9b5 RS |
1314 | @defvar mode-line-mule-info |
1315 | This variable holds the value of the mode-line construct that displays | |
1316 | information about the language environment, buffer coding system, and | |
a9f0a989 | 1317 | current input method. @xref{Non-ASCII Characters}. |
969fe9b5 RS |
1318 | @end defvar |
1319 | ||
a44af9f2 | 1320 | @defvar mode-line-modified |
de9f0bd9 | 1321 | This variable holds the value of the mode-line construct that displays |
a44af9f2 RS |
1322 | whether the current buffer is modified. |
1323 | ||
969fe9b5 RS |
1324 | The default value of @code{mode-line-modified} is @code{("%1*%1+")}. |
1325 | This means that the mode line displays @samp{**} if the buffer is | |
1326 | modified, @samp{--} if the buffer is not modified, @samp{%%} if the | |
1327 | buffer is read only, and @samp{%*} if the buffer is read only and | |
1328 | modified. | |
a44af9f2 RS |
1329 | |
1330 | Changing this variable does not force an update of the mode line. | |
1331 | @end defvar | |
1332 | ||
969fe9b5 RS |
1333 | @defvar mode-line-frame-identification |
1334 | This variable identifies the current frame. The default value is | |
1335 | @code{" "} if you are using a window system which can show multiple | |
1336 | frames, or @code{"-%F "} on an ordinary terminal which shows only one | |
1337 | frame at a time. | |
1338 | @end defvar | |
1339 | ||
a44af9f2 | 1340 | @defvar mode-line-buffer-identification |
de9f0bd9 | 1341 | This variable identifies the buffer being displayed in the window. Its |
ebc6903b RS |
1342 | default value is @code{("%12b")}, which displays the buffer name, padded |
1343 | with spaces to at least 12 columns. | |
a44af9f2 RS |
1344 | @end defvar |
1345 | ||
1346 | @defvar global-mode-string | |
1347 | This variable holds a mode line spec that appears in the mode line by | |
1348 | default, just after the buffer name. The command @code{display-time} | |
1349 | sets @code{global-mode-string} to refer to the variable | |
1350 | @code{display-time-string}, which holds a string containing the time and | |
1351 | load information. | |
1352 | ||
1353 | The @samp{%M} construct substitutes the value of | |
f9f59935 RS |
1354 | @code{global-mode-string}, but that is obsolete, since the variable is |
1355 | included in the mode line from @code{mode-line-format}. | |
a44af9f2 RS |
1356 | @end defvar |
1357 | ||
1358 | @defvar mode-name | |
de9f0bd9 | 1359 | This buffer-local variable holds the ``pretty'' name of the current |
a44af9f2 RS |
1360 | buffer's major mode. Each major mode should set this variable so that the |
1361 | mode name will appear in the mode line. | |
1362 | @end defvar | |
1363 | ||
1364 | @defvar minor-mode-alist | |
de9f0bd9 | 1365 | This variable holds an association list whose elements specify how the |
a44af9f2 RS |
1366 | mode line should indicate that a minor mode is active. Each element of |
1367 | the @code{minor-mode-alist} should be a two-element list: | |
1368 | ||
1369 | @example | |
1370 | (@var{minor-mode-variable} @var{mode-line-string}) | |
1371 | @end example | |
1372 | ||
1373 | More generally, @var{mode-line-string} can be any mode line spec. It | |
1374 | appears in the mode line when the value of @var{minor-mode-variable} is | |
1375 | non-@code{nil}, and not otherwise. These strings should begin with | |
1376 | spaces so that they don't run together. Conventionally, the | |
1377 | @var{minor-mode-variable} for a specific mode is set to a non-@code{nil} | |
1378 | value when that minor mode is activated. | |
1379 | ||
1380 | The default value of @code{minor-mode-alist} is: | |
1381 | ||
1382 | @example | |
1383 | @group | |
1384 | minor-mode-alist | |
bfe721d1 | 1385 | @result{} ((vc-mode vc-mode) |
177c0ea7 JB |
1386 | (abbrev-mode " Abbrev") |
1387 | (overwrite-mode overwrite-mode) | |
1388 | (auto-fill-function " Fill") | |
bfe721d1 KH |
1389 | (defining-kbd-macro " Def") |
1390 | (isearch-mode isearch-mode)) | |
a44af9f2 RS |
1391 | @end group |
1392 | @end example | |
1393 | ||
f9f59935 RS |
1394 | @code{minor-mode-alist} itself is not buffer-local. Each variable |
1395 | mentioned in the alist should be buffer-local if its minor mode can be | |
1396 | enabled separately in each buffer. | |
a44af9f2 RS |
1397 | @end defvar |
1398 | ||
1399 | @defvar mode-line-process | |
1400 | This buffer-local variable contains the mode line information on process | |
1401 | status in modes used for communicating with subprocesses. It is | |
1402 | displayed immediately following the major mode name, with no intervening | |
1403 | space. For example, its value in the @samp{*shell*} buffer is | |
1911e6e5 | 1404 | @code{(":%s")}, which allows the shell to display its status along |
a40d4712 | 1405 | with the major mode as: @samp{(Shell:run)}. Normally this variable |
a44af9f2 RS |
1406 | is @code{nil}. |
1407 | @end defvar | |
1408 | ||
a40d4712 PR |
1409 | Some variables are used by @code{minor-mode-alist} to display |
1410 | a string for various minor modes when enabled. This is a typical | |
1411 | example: | |
1412 | ||
1413 | @defvar vc-mode | |
1414 | The variable @code{vc-mode}, buffer-local in each buffer, records | |
1415 | whether the buffer's visited file is maintained with version control, | |
1416 | and, if so, which kind. Its value is a string that appears in the mode | |
1417 | line, or @code{nil} for no version control. | |
1418 | @end defvar | |
1419 | ||
1420 | The variable @code{default-mode-line-format} is where | |
1421 | @code{mode-line-format} usually gets its value: | |
1422 | ||
a44af9f2 | 1423 | @defvar default-mode-line-format |
de9f0bd9 | 1424 | This variable holds the default @code{mode-line-format} for buffers |
a44af9f2 RS |
1425 | that do not override it. This is the same as @code{(default-value |
1426 | 'mode-line-format)}. | |
1427 | ||
f9f59935 | 1428 | The default value of @code{default-mode-line-format} is this list: |
a44af9f2 RS |
1429 | |
1430 | @example | |
1431 | @group | |
f9f59935 RS |
1432 | ("-" |
1433 | mode-line-mule-info | |
a44af9f2 | 1434 | mode-line-modified |
f9f59935 | 1435 | mode-line-frame-identification |
a44af9f2 | 1436 | mode-line-buffer-identification |
f9f59935 | 1437 | @end group |
a44af9f2 RS |
1438 | " " |
1439 | global-mode-string | |
f9f59935 | 1440 | @group |
a44af9f2 | 1441 | " %[(" |
a40d4712 | 1442 | ;; @r{@code{mode-line-mode-name} is a function} |
513331d3 | 1443 | ;; @r{that copies the mode name and adds text} |
a40d4712 | 1444 | ;; @r{properties to make it mouse-sensitive.} |
8241495d | 1445 | (:eval (mode-line-mode-name)) |
bfe721d1 | 1446 | mode-line-process |
177c0ea7 JB |
1447 | minor-mode-alist |
1448 | "%n" | |
f9f59935 RS |
1449 | ")%]--" |
1450 | @end group | |
1451 | @group | |
1452 | (which-func-mode ("" which-func-format "--")) | |
bfe721d1 | 1453 | (line-number-mode "L%l--") |
f9f59935 | 1454 | (column-number-mode "C%c--") |
a44af9f2 RS |
1455 | (-3 . "%p") |
1456 | "-%-") | |
1457 | @end group | |
1458 | @end example | |
1459 | @end defvar | |
1460 | ||
1461 | @node %-Constructs | |
1462 | @subsection @code{%}-Constructs in the Mode Line | |
1463 | ||
1464 | The following table lists the recognized @code{%}-constructs and what | |
de9f0bd9 RS |
1465 | they mean. In any construct except @samp{%%}, you can add a decimal |
1466 | integer after the @samp{%} to specify how many characters to display. | |
a44af9f2 RS |
1467 | |
1468 | @table @code | |
1469 | @item %b | |
1470 | The current buffer name, obtained with the @code{buffer-name} function. | |
1471 | @xref{Buffer Names}. | |
1472 | ||
a40d4712 PR |
1473 | @item %c |
1474 | The current column number of point. | |
1475 | ||
a44af9f2 RS |
1476 | @item %f |
1477 | The visited file name, obtained with the @code{buffer-file-name} | |
1478 | function. @xref{Buffer File Name}. | |
1479 | ||
22697dac | 1480 | @item %F |
969fe9b5 RS |
1481 | The title (only on a window system) or the name of the selected frame. |
1482 | @xref{Window Frame Parameters}. | |
22697dac | 1483 | |
22697dac | 1484 | @item %l |
8241495d RS |
1485 | The current line number of point, counting within the accessible portion |
1486 | of the buffer. | |
22697dac | 1487 | |
a40d4712 PR |
1488 | @item %n |
1489 | @samp{Narrow} when narrowing is in effect; nothing otherwise (see | |
1490 | @code{narrow-to-region} in @ref{Narrowing}). | |
1491 | ||
1492 | @item %p | |
1493 | The percentage of the buffer text above the @strong{top} of window, or | |
1494 | @samp{Top}, @samp{Bottom} or @samp{All}. Note that the default | |
1495 | mode-line specification truncates this to three characters. | |
1496 | ||
1497 | @item %P | |
1498 | The percentage of the buffer text that is above the @strong{bottom} of | |
1499 | the window (which includes the text visible in the window, as well as | |
1500 | the text above the top), plus @samp{Top} if the top of the buffer is | |
1501 | visible on screen; or @samp{Bottom} or @samp{All}. | |
1502 | ||
1503 | @item %s | |
1504 | The status of the subprocess belonging to the current buffer, obtained with | |
1505 | @code{process-status}. @xref{Process Information}. | |
1506 | ||
1507 | @item %t | |
1508 | Whether the visited file is a text file or a binary file. This is a | |
1509 | meaningful distinction only on certain operating systems (@pxref{MS-DOS | |
1510 | File Types}). | |
1511 | ||
a44af9f2 RS |
1512 | @item %* |
1513 | @samp{%} if the buffer is read only (see @code{buffer-read-only}); @* | |
1514 | @samp{*} if the buffer is modified (see @code{buffer-modified-p}); @* | |
1515 | @samp{-} otherwise. @xref{Buffer Modification}. | |
1516 | ||
1517 | @item %+ | |
22697dac KH |
1518 | @samp{*} if the buffer is modified (see @code{buffer-modified-p}); @* |
1519 | @samp{%} if the buffer is read only (see @code{buffer-read-only}); @* | |
1520 | @samp{-} otherwise. This differs from @samp{%*} only for a modified | |
1521 | read-only buffer. @xref{Buffer Modification}. | |
1522 | ||
1523 | @item %& | |
de9f0bd9 | 1524 | @samp{*} if the buffer is modified, and @samp{-} otherwise. |
a44af9f2 | 1525 | |
a44af9f2 RS |
1526 | @item %[ |
1527 | An indication of the depth of recursive editing levels (not counting | |
1528 | minibuffer levels): one @samp{[} for each editing level. | |
1529 | @xref{Recursive Editing}. | |
1530 | ||
1531 | @item %] | |
1532 | One @samp{]} for each recursive editing level (not counting minibuffer | |
1533 | levels). | |
1534 | ||
a40d4712 PR |
1535 | @item %- |
1536 | Dashes sufficient to fill the remainder of the mode line. | |
1537 | ||
a44af9f2 RS |
1538 | @item %% |
1539 | The character @samp{%}---this is how to include a literal @samp{%} in a | |
1540 | string in which @code{%}-constructs are allowed. | |
a44af9f2 RS |
1541 | @end table |
1542 | ||
1543 | The following two @code{%}-constructs are still supported, but they are | |
1544 | obsolete, since you can get the same results with the variables | |
1545 | @code{mode-name} and @code{global-mode-string}. | |
1546 | ||
1547 | @table @code | |
1548 | @item %m | |
1549 | The value of @code{mode-name}. | |
1550 | ||
1551 | @item %M | |
1552 | The value of @code{global-mode-string}. Currently, only | |
1553 | @code{display-time} modifies the value of @code{global-mode-string}. | |
1554 | @end table | |
1555 | ||
8241495d RS |
1556 | @node Properties in Mode |
1557 | @subsection Properties in the Mode Line | |
1558 | ||
1559 | Starting in Emacs 21, certain text properties are meaningful in the | |
1560 | mode line. The @code{face} property affects the appearance of text; the | |
1561 | @code{help-echo} property associate help strings with the text, and | |
ce75fd23 | 1562 | @code{local-map} can make the text mouse-sensitive. |
8241495d RS |
1563 | |
1564 | There are three ways to specify text properties for text in the mode | |
1565 | line: | |
1566 | ||
1567 | @enumerate | |
1568 | @item | |
ce75fd23 GM |
1569 | Put a string with the @code{local-map} property directly into the |
1570 | mode-line data structure. | |
8241495d RS |
1571 | |
1572 | @item | |
ce75fd23 GM |
1573 | Put a @code{local-map} property on a mode-line %-construct |
1574 | such as @samp{%12b}; then the expansion of the %-construct | |
1575 | will have that same text property. | |
8241495d RS |
1576 | |
1577 | @item | |
1578 | Use a list containing @code{:eval @var{form}} in the mode-line data | |
1579 | structure, and make @var{form} evaluate to a string that has a | |
ce75fd23 | 1580 | @code{local-map} property. |
8241495d RS |
1581 | @end enumerate |
1582 | ||
ce75fd23 | 1583 | You use the @code{local-map} property to specify a keymap. Like any |
8241495d | 1584 | keymap, it can bind character keys and function keys; but that has no |
a40d4712 | 1585 | effect, since it is impossible to move point into the mode line. This |
8241495d RS |
1586 | keymap can only take real effect for mouse clicks. |
1587 | ||
1588 | @node Header Lines | |
1589 | @subsection Window Header Lines | |
1590 | @cindex header line (of a window) | |
1591 | @cindex window header line | |
1592 | ||
1593 | Starting in Emacs 21, a window can have a @dfn{header line} at the | |
1594 | top, just as it can have a mode line at the bottom. The header line | |
1595 | feature works just like the mode line feature, except that it's | |
1596 | controlled by different variables. | |
1597 | ||
1598 | @tindex header-line-format | |
1599 | @defvar header-line-format | |
1600 | This variable, local in every buffer, specifies how to display the | |
1601 | header line, for windows displaying the buffer. The format of the value | |
13ede7fc | 1602 | is the same as for @code{mode-line-format} (@pxref{Mode Line Data}). |
8241495d RS |
1603 | @end defvar |
1604 | ||
1605 | @tindex default-header-line-format | |
1606 | @defvar default-header-line-format | |
1607 | This variable holds the default @code{header-line-format} for buffers | |
1608 | that do not override it. This is the same as @code{(default-value | |
1609 | 'header-line-format)}. | |
1610 | ||
1611 | It is normally @code{nil}, so that ordinary buffers have no header line. | |
1612 | @end defvar | |
1613 | ||
bda7c6dd | 1614 | @node Emulating Mode Line |
3ebe0346 | 1615 | @subsection Emulating Mode Line Formatting |
bda7c6dd RS |
1616 | |
1617 | You can use the function @code{format-mode-line} to compute | |
1618 | the text that would appear in a mode line or header line | |
1619 | based on certain mode line specification. | |
1620 | ||
1621 | @defun format-mode-line &optional format window no-props | |
1622 | This function formats a line of text according to @var{format} as if | |
1623 | it were generating the mode line for @var{window}, but instead of | |
1624 | displaying the text in the mode line or the header line, it returns | |
1625 | the text as a string. | |
1626 | ||
1627 | If @var{format} is @code{nil}, that means to use | |
1628 | @code{mode-line-format} and return the text that would appear in the | |
1629 | mode line. If @var{format} is @code{t}, that means to use | |
1630 | @code{header-line-format} so as to return the text that would appear | |
1631 | in the header line (@code{""} if the window has no header line). | |
1632 | The argument @var{window} defaults to the selected window. | |
1633 | ||
1634 | The value string normally has text properties that correspond to the | |
1635 | faces, keymaps, etc., that the mode line would have. If | |
1636 | @var{no-props} is non-@code{nil}, the value has no text properties. | |
1637 | @end defun | |
1638 | ||
f9f59935 RS |
1639 | @node Imenu |
1640 | @section Imenu | |
1641 | ||
1642 | @cindex Imenu | |
969fe9b5 RS |
1643 | @dfn{Imenu} is a feature that lets users select a definition or |
1644 | section in the buffer, from a menu which lists all of them, to go | |
5a5d2aec RS |
1645 | directly to that location in the buffer. Imenu works by constructing |
1646 | a buffer index which lists the names and buffer positions of the | |
a40d4712 | 1647 | definitions, or other named portions of the buffer; then the user can |
5a5d2aec RS |
1648 | choose one of them and move point to it. The user-level commands for |
1649 | using Imenu are described in the Emacs Manual (@pxref{Imenu,, Imenu, | |
1650 | emacs, the Emacs Manual}). This section explains how to customize | |
1651 | Imenu's method of finding definitions or buffer portions for a | |
a40d4712 | 1652 | particular major mode. |
969fe9b5 RS |
1653 | |
1654 | The usual and simplest way is to set the variable | |
1655 | @code{imenu-generic-expression}: | |
f9f59935 RS |
1656 | |
1657 | @defvar imenu-generic-expression | |
1658 | This variable, if non-@code{nil}, specifies regular expressions for | |
1659 | finding definitions for Imenu. In the simplest case, elements should | |
1660 | look like this: | |
1661 | ||
1662 | @example | |
1663 | (@var{menu-title} @var{regexp} @var{subexp}) | |
1664 | @end example | |
1665 | ||
1666 | Here, if @var{menu-title} is non-@code{nil}, it says that the matches | |
1667 | for this element should go in a submenu of the buffer index; | |
1668 | @var{menu-title} itself specifies the name for the submenu. If | |
1669 | @var{menu-title} is @code{nil}, the matches for this element go directly | |
1670 | in the top level of the buffer index. | |
1671 | ||
1672 | The second item in the list, @var{regexp}, is a regular expression | |
8241495d | 1673 | (@pxref{Regular Expressions}); anything in the buffer that it matches is |
a40d4712 PR |
1674 | considered a definition, something to mention in the buffer index. The |
1675 | third item, @var{subexp}, indicates which subexpression in @var{regexp} | |
8241495d | 1676 | matches the definition's name. |
f9f59935 RS |
1677 | |
1678 | An element can also look like this: | |
1679 | ||
1680 | @example | |
1681 | (@var{menu-title} @var{regexp} @var{index} @var{function} @var{arguments}@dots{}) | |
1682 | @end example | |
1683 | ||
1684 | Each match for this element creates a special index item which, if | |
a40d4712 PR |
1685 | selected by the user, calls @var{function} with arguments consisting of |
1686 | the item name, the buffer position, and @var{arguments}. | |
f9f59935 RS |
1687 | |
1688 | For Emacs Lisp mode, @var{pattern} could look like this: | |
1689 | ||
a9f0a989 | 1690 | @c should probably use imenu-syntax-alist and \\sw rather than [-A-Za-z0-9+] |
f9f59935 RS |
1691 | @example |
1692 | @group | |
1693 | ((nil "^\\s-*(def\\(un\\|subst\\|macro\\|advice\\)\ | |
1694 | \\s-+\\([-A-Za-z0-9+]+\\)" 2) | |
1695 | @end group | |
1696 | @group | |
1697 | ("*Vars*" "^\\s-*(def\\(var\\|const\\)\ | |
1698 | \\s-+\\([-A-Za-z0-9+]+\\)" 2) | |
1699 | @end group | |
1700 | @group | |
1701 | ("*Types*" | |
a9f0a989 RS |
1702 | "^\\s-*\ |
1703 | (def\\(type\\|struct\\|class\\|ine-condition\\)\ | |
f9f59935 RS |
1704 | \\s-+\\([-A-Za-z0-9+]+\\)" 2)) |
1705 | @end group | |
1706 | @end example | |
1707 | ||
969fe9b5 | 1708 | Setting this variable makes it buffer-local in the current buffer. |
f9f59935 RS |
1709 | @end defvar |
1710 | ||
1711 | @defvar imenu-case-fold-search | |
a9f0a989 RS |
1712 | This variable controls whether matching against |
1713 | @var{imenu-generic-expression} is case-sensitive: @code{t}, the default, | |
1714 | means matching should ignore case. | |
1715 | ||
1716 | Setting this variable makes it buffer-local in the current buffer. | |
1717 | @end defvar | |
1718 | ||
1719 | @defvar imenu-syntax-alist | |
1720 | This variable is an alist of syntax table modifiers to use while | |
1911e6e5 RS |
1721 | processing @code{imenu-generic-expression}, to override the syntax table |
1722 | of the current buffer. Each element should have this form: | |
a9f0a989 RS |
1723 | |
1724 | @example | |
1725 | (@var{characters} . @var{syntax-description}) | |
1726 | @end example | |
1727 | ||
1728 | The @sc{car}, @var{characters}, can be either a character or a string. | |
1729 | The element says to give that character or characters the syntax | |
1730 | specified by @var{syntax-description}, which is passed to | |
1731 | @code{modify-syntax-entry} (@pxref{Syntax Table Functions}). | |
1732 | ||
1733 | This feature is typically used to give word syntax to characters which | |
1734 | normally have symbol syntax, and thus to simplify | |
1735 | @code{imenu-generic-expression} and speed up matching. | |
1736 | For example, Fortran mode uses it this way: | |
1737 | ||
1738 | @example | |
5a5d2aec | 1739 | (setq imenu-syntax-alist '(("_$" . "w"))) |
a9f0a989 RS |
1740 | @end example |
1741 | ||
1742 | The @code{imenu-generic-expression} patterns can then use @samp{\\sw+} | |
1911e6e5 | 1743 | instead of @samp{\\(\\sw\\|\\s_\\)+}. Note that this technique may be |
8241495d | 1744 | inconvenient when the mode needs to limit the initial character |
ebc6903b RS |
1745 | of a name to a smaller set of characters than are allowed in the rest |
1746 | of a name. | |
f9f59935 | 1747 | |
969fe9b5 | 1748 | Setting this variable makes it buffer-local in the current buffer. |
f9f59935 RS |
1749 | @end defvar |
1750 | ||
1751 | Another way to customize Imenu for a major mode is to set the | |
1752 | variables @code{imenu-prev-index-position-function} and | |
969fe9b5 | 1753 | @code{imenu-extract-index-name-function}: |
f9f59935 RS |
1754 | |
1755 | @defvar imenu-prev-index-position-function | |
05aea714 | 1756 | If this variable is non-@code{nil}, its value should be a function that |
a40d4712 PR |
1757 | finds the next ``definition'' to put in the buffer index, scanning |
1758 | backward in the buffer from point. It should return @code{nil} if it | |
5fe3b9bc | 1759 | doesn't find another ``definition'' before point. Otherwise it should |
a40d4712 PR |
1760 | leave point at the place it finds a ``definition,'' and return any |
1761 | non-@code{nil} value. | |
f9f59935 | 1762 | |
969fe9b5 | 1763 | Setting this variable makes it buffer-local in the current buffer. |
f9f59935 RS |
1764 | @end defvar |
1765 | ||
1766 | @defvar imenu-extract-index-name-function | |
1767 | If this variable is non-@code{nil}, its value should be a function to | |
969fe9b5 RS |
1768 | return the name for a definition, assuming point is in that definition |
1769 | as the @code{imenu-prev-index-position-function} function would leave | |
1770 | it. | |
f9f59935 | 1771 | |
969fe9b5 | 1772 | Setting this variable makes it buffer-local in the current buffer. |
f9f59935 RS |
1773 | @end defvar |
1774 | ||
969fe9b5 | 1775 | The last way to customize Imenu for a major mode is to set the |
a40d4712 | 1776 | variable @code{imenu-create-index-function}: |
969fe9b5 | 1777 | |
f9f59935 RS |
1778 | @defvar imenu-create-index-function |
1779 | This variable specifies the function to use for creating a buffer index. | |
1780 | The function should take no arguments, and return an index for the | |
1781 | current buffer. It is called within @code{save-excursion}, so where it | |
1782 | leaves point makes no difference. | |
1783 | ||
1784 | The default value is a function that uses | |
1785 | @code{imenu-generic-expression} to produce the index alist. If you | |
1786 | specify a different function, then @code{imenu-generic-expression} is | |
1787 | not used. | |
1788 | ||
969fe9b5 | 1789 | Setting this variable makes it buffer-local in the current buffer. |
f9f59935 RS |
1790 | @end defvar |
1791 | ||
1792 | @defvar imenu-index-alist | |
1793 | This variable holds the index alist for the current buffer. | |
969fe9b5 | 1794 | Setting it makes it buffer-local in the current buffer. |
f9f59935 RS |
1795 | |
1796 | Simple elements in the alist look like @code{(@var{index-name} | |
1797 | . @var{index-position})}. Selecting a simple element has the effect of | |
1798 | moving to position @var{index-position} in the buffer. | |
1799 | ||
1800 | Special elements look like @code{(@var{index-name} @var{position} | |
1801 | @var{function} @var{arguments}@dots{})}. Selecting a special element | |
1802 | performs | |
1803 | ||
1804 | @example | |
1805 | (funcall @var{function} @var{index-name} @var{position} @var{arguments}@dots{}) | |
1806 | @end example | |
1807 | ||
1808 | A nested sub-alist element looks like @code{(@var{index-name} | |
1809 | @var{sub-alist})}. | |
1810 | @end defvar | |
1811 | ||
1812 | @node Font Lock Mode | |
1813 | @section Font Lock Mode | |
1814 | @cindex Font Lock Mode | |
1815 | ||
1816 | @dfn{Font Lock mode} is a feature that automatically attaches | |
1817 | @code{face} properties to certain parts of the buffer based on their | |
1818 | syntactic role. How it parses the buffer depends on the major mode; | |
a40d4712 | 1819 | most major modes define syntactic criteria for which faces to use in |
969fe9b5 | 1820 | which contexts. This section explains how to customize Font Lock for a |
a40d4712 | 1821 | particular major mode. |
f9f59935 RS |
1822 | |
1823 | Font Lock mode finds text to highlight in two ways: through syntactic | |
1824 | parsing based on the syntax table, and through searching (usually for | |
1825 | regular expressions). Syntactic fontification happens first; it finds | |
1826 | comments and string constants, and highlights them using | |
1827 | @code{font-lock-comment-face} and @code{font-lock-string-face} | |
a40d4712 | 1828 | (@pxref{Faces for Font Lock}). Search-based fontification follows. |
f9f59935 RS |
1829 | |
1830 | @menu | |
1831 | * Font Lock Basics:: | |
1832 | * Search-based Fontification:: | |
1833 | * Other Font Lock Variables:: | |
1834 | * Levels of Font Lock:: | |
651f7556 | 1835 | * Precalculated Fontification:: |
f9f59935 | 1836 | * Faces for Font Lock:: |
969fe9b5 | 1837 | * Syntactic Font Lock:: |
f9f59935 RS |
1838 | @end menu |
1839 | ||
1840 | @node Font Lock Basics | |
1841 | @subsection Font Lock Basics | |
1842 | ||
1843 | There are several variables that control how Font Lock mode highlights | |
1844 | text. But major modes should not set any of these variables directly. | |
86494bd5 | 1845 | Instead, they should set @code{font-lock-defaults} as a buffer-local |
969fe9b5 RS |
1846 | variable. The value assigned to this variable is used, if and when Font |
1847 | Lock mode is enabled, to set all the other variables. | |
f9f59935 RS |
1848 | |
1849 | @defvar font-lock-defaults | |
1850 | This variable is set by major modes, as a buffer-local variable, to | |
1851 | specify how to fontify text in that mode. The value should look like | |
1852 | this: | |
1853 | ||
1854 | @example | |
1855 | (@var{keywords} @var{keywords-only} @var{case-fold} | |
1856 | @var{syntax-alist} @var{syntax-begin} @var{other-vars}@dots{}) | |
1857 | @end example | |
1858 | ||
1859 | The first element, @var{keywords}, indirectly specifies the value of | |
1860 | @code{font-lock-keywords}. It can be a symbol, a variable whose value | |
a40d4712 | 1861 | is the list to use for @code{font-lock-keywords}. It can also be a list of |
f9f59935 RS |
1862 | several such symbols, one for each possible level of fontification. The |
1863 | first symbol specifies how to do level 1 fontification, the second | |
1864 | symbol how to do level 2, and so on. | |
1865 | ||
1866 | The second element, @var{keywords-only}, specifies the value of the | |
a9f0a989 | 1867 | variable @code{font-lock-keywords-only}. If this is non-@code{nil}, |
969fe9b5 | 1868 | syntactic fontification (of strings and comments) is not performed. |
f9f59935 RS |
1869 | |
1870 | The third element, @var{case-fold}, specifies the value of | |
1871 | @code{font-lock-case-fold-search}. If it is non-@code{nil}, Font Lock | |
969fe9b5 RS |
1872 | mode ignores case when searching as directed by |
1873 | @code{font-lock-keywords}. | |
f9f59935 RS |
1874 | |
1875 | If the fourth element, @var{syntax-alist}, is non-@code{nil}, it should be | |
1876 | a list of cons cells of the form @code{(@var{char-or-string} | |
1877 | . @var{string})}. These are used to set up a syntax table for | |
1878 | fontification (@pxref{Syntax Table Functions}). The resulting syntax | |
1879 | table is stored in @code{font-lock-syntax-table}. | |
1880 | ||
1881 | The fifth element, @var{syntax-begin}, specifies the value of | |
969fe9b5 | 1882 | @code{font-lock-beginning-of-syntax-function} (see below). |
f9f59935 | 1883 | |
a40d4712 PR |
1884 | All the remaining elements (if any) are collectively called |
1885 | @var{other-vars}. Each of these elements should have the form | |
1886 | @code{(@var{variable} . @var{value})}---which means, make @var{variable} | |
1887 | buffer-local and then set it to @var{value}. You can use these | |
1888 | @var{other-vars} to set other variables that affect fontification, | |
1889 | aside from those you can control with the first five elements. | |
f9f59935 RS |
1890 | @end defvar |
1891 | ||
1892 | @node Search-based Fontification | |
1893 | @subsection Search-based Fontification | |
1894 | ||
1895 | The most important variable for customizing Font Lock mode is | |
1896 | @code{font-lock-keywords}. It specifies the search criteria for | |
1897 | search-based fontification. | |
1898 | ||
1899 | @defvar font-lock-keywords | |
1900 | This variable's value is a list of the keywords to highlight. Be | |
969fe9b5 RS |
1901 | careful when composing regular expressions for this list; a poorly |
1902 | written pattern can dramatically slow things down! | |
f9f59935 RS |
1903 | @end defvar |
1904 | ||
1905 | Each element of @code{font-lock-keywords} specifies how to find | |
969fe9b5 RS |
1906 | certain cases of text, and how to highlight those cases. Font Lock mode |
1907 | processes the elements of @code{font-lock-keywords} one by one, and for | |
1908 | each element, it finds and handles all matches. Ordinarily, once | |
1909 | part of the text has been fontified already, this cannot be overridden | |
1910 | by a subsequent match in the same text; but you can specify different | |
1911 | behavior using the @var{override} element of a @var{highlighter}. | |
1912 | ||
1913 | Each element of @code{font-lock-keywords} should have one of these | |
1914 | forms: | |
f9f59935 RS |
1915 | |
1916 | @table @code | |
1917 | @item @var{regexp} | |
1918 | Highlight all matches for @var{regexp} using | |
1919 | @code{font-lock-keyword-face}. For example, | |
1920 | ||
1921 | @example | |
1922 | ;; @r{Highlight discrete occurrences of @samp{foo}} | |
1923 | ;; @r{using @code{font-lock-keyword-face}.} | |
1924 | "\\<foo\\>" | |
1925 | @end example | |
1926 | ||
969fe9b5 RS |
1927 | The function @code{regexp-opt} (@pxref{Syntax of Regexps}) is useful for |
1928 | calculating optimal regular expressions to match a number of different | |
1929 | keywords. | |
f9f59935 RS |
1930 | |
1931 | @item @var{function} | |
1932 | Find text by calling @var{function}, and highlight the matches | |
1933 | it finds using @code{font-lock-keyword-face}. | |
1934 | ||
1935 | When @var{function} is called, it receives one argument, the limit of | |
07f7b41c RS |
1936 | the search; it should searching at point, and not search beyond the |
1937 | limit. It should return non-@code{nil} if it succeeds, and set the | |
1938 | match data to describe the match that was found. Returning @code{nil} | |
1939 | indicates failure of the search. | |
1940 | ||
1941 | Fontification will call @var{function} repeatedly with the same limit, | |
1942 | and with point where the previous invocation left it, until | |
1943 | @var{function} fails. On failure, @var{function} need not reset point | |
1944 | in any particular way. | |
f9f59935 RS |
1945 | |
1946 | @item (@var{matcher} . @var{match}) | |
86494bd5 | 1947 | In this kind of element, @var{matcher} is either a regular |
f9f59935 RS |
1948 | expression or a function, as described above. The @sc{cdr}, |
1949 | @var{match}, specifies which subexpression of @var{matcher} should be | |
969fe9b5 | 1950 | highlighted (instead of the entire text that @var{matcher} matched). |
f9f59935 RS |
1951 | |
1952 | @example | |
8241495d | 1953 | ;; @r{Highlight the @samp{bar} in each occurrence of @samp{fubar},} |
f9f59935 RS |
1954 | ;; @r{using @code{font-lock-keyword-face}.} |
1955 | ("fu\\(bar\\)" . 1) | |
1956 | @end example | |
1957 | ||
969fe9b5 | 1958 | If you use @code{regexp-opt} to produce the regular expression |
f9f59935 RS |
1959 | @var{matcher}, then you can use @code{regexp-opt-depth} (@pxref{Syntax |
1960 | of Regexps}) to calculate the value for @var{match}. | |
1961 | ||
1962 | @item (@var{matcher} . @var{facename}) | |
1963 | In this kind of element, @var{facename} is an expression whose value | |
1964 | specifies the face name to use for highlighting. | |
1965 | ||
1966 | @example | |
1967 | ;; @r{Highlight occurrences of @samp{fubar},} | |
1968 | ;; @r{using the face which is the value of @code{fubar-face}.} | |
1969 | ("fubar" . fubar-face) | |
1970 | @end example | |
1971 | ||
fdba9ef4 RS |
1972 | The value of @var{facename} is usually a face name (a symbol), but it |
1973 | can also be a list of the form | |
1974 | ||
1975 | @example | |
1976 | (face @var{face} @var{prop1} @var{val1} @var{prop2} @var{val2}@dots{}) | |
1977 | @end example | |
1978 | ||
1979 | to specify various text properties to put on the text that matches. | |
1980 | If you do this, be sure to add the other text property names that you | |
1981 | set in this way to the value of @code{font-lock-extra-managed-props} | |
1982 | so that the properties will also be cleared out when they are no longer | |
1983 | appropriate. | |
1984 | ||
f9f59935 RS |
1985 | @item (@var{matcher} . @var{highlighter}) |
1986 | In this kind of element, @var{highlighter} is a list | |
1987 | which specifies how to highlight matches found by @var{matcher}. | |
1988 | It has the form | |
1989 | ||
1990 | @example | |
1991 | (@var{subexp} @var{facename} @var{override} @var{laxmatch}) | |
1992 | @end example | |
1993 | ||
1994 | The @sc{car}, @var{subexp}, is an integer specifying which subexpression | |
969fe9b5 RS |
1995 | of the match to fontify (0 means the entire matching text). The second |
1996 | subelement, @var{facename}, specifies the face, as described above. | |
f9f59935 RS |
1997 | |
1998 | The last two values in @var{highlighter}, @var{override} and | |
bda7c6dd RS |
1999 | @var{laxmatch}, are flags. If @var{override} is @code{t}, this |
2000 | element can override existing fontification made by previous elements | |
2001 | of @code{font-lock-keywords}. If it is @code{keep}, then each | |
2002 | character is fontified if it has not been fontified already by some | |
2003 | other element. If it is @code{prepend}, the face @var{facename} is | |
2004 | added to the beginning of the @code{font-lock-face} property. If it | |
2005 | is @code{append}, the face @var{facename} is added to the end of the | |
2006 | @code{font-lock-face} property. | |
f9f59935 RS |
2007 | |
2008 | If @var{laxmatch} is non-@code{nil}, it means there should be no error | |
2009 | if there is no subexpression numbered @var{subexp} in @var{matcher}. | |
99b62845 GM |
2010 | Obviously, fontification of the subexpression numbered @var{subexp} will |
2011 | not occur. However, fontification of other subexpressions (and other | |
2012 | regexps) will continue. If @var{laxmatch} is @code{nil}, and the | |
2013 | specified subexpression is missing, then an error is signalled which | |
2014 | terminates search-based fontification. | |
f9f59935 RS |
2015 | |
2016 | Here are some examples of elements of this kind, and what they do: | |
2017 | ||
2018 | @smallexample | |
2019 | ;; @r{Highlight occurrences of either @samp{foo} or @samp{bar},} | |
2020 | ;; @r{using @code{foo-bar-face}, even if they have already been highlighted.} | |
2021 | ;; @r{@code{foo-bar-face} should be a variable whose value is a face.} | |
2022 | ("foo\\|bar" 0 foo-bar-face t) | |
2023 | ||
8241495d | 2024 | ;; @r{Highlight the first subexpression within each occurrence} |
f9f59935 RS |
2025 | ;; @r{that the function @code{fubar-match} finds,} |
2026 | ;; @r{using the face which is the value of @code{fubar-face}.} | |
2027 | (fubar-match 1 fubar-face) | |
2028 | @end smallexample | |
2029 | ||
2030 | @item (@var{matcher} @var{highlighters}@dots{}) | |
2031 | This sort of element specifies several @var{highlighter} lists for a | |
2032 | single @var{matcher}. In order for this to be useful, each | |
2033 | @var{highlighter} should have a different value of @var{subexp}; that is, | |
2034 | each one should apply to a different subexpression of @var{matcher}. | |
2035 | ||
2036 | @ignore | |
2037 | @item (@var{matcher} . @var{anchored}) | |
2038 | In this kind of element, @var{anchored} acts much like a | |
2039 | @var{highlighter}, but it is more complex and can specify multiple | |
2040 | successive searches. | |
2041 | ||
2042 | For highlighting single items, typically only @var{highlighter} is | |
2043 | required. However, if an item or (typically) items are to be | |
2044 | highlighted following the instance of another item (the anchor) then | |
2045 | @var{anchored} may be required. | |
2046 | ||
2047 | It has this format: | |
2048 | ||
2049 | @example | |
2050 | (@var{submatcher} @var{pre-match-form} @var{post-match-form} @var{highlighters}@dots{}) | |
2051 | @end example | |
2052 | ||
2053 | @c I can't parse this text -- rms | |
2054 | where @var{submatcher} is much like @var{matcher}, with one | |
2055 | exception---see below. @var{pre-match-form} and @var{post-match-form} | |
2056 | are evaluated before the first, and after the last, instance | |
2057 | @var{anchored}'s @var{submatcher} is used. Therefore they can be used | |
a9f0a989 | 2058 | to initialize before, and cleanup after, @var{submatcher} is used. |
f9f59935 RS |
2059 | Typically, @var{pre-match-form} is used to move to some position |
2060 | relative to the original @var{submatcher}, before starting with | |
2061 | @var{anchored}'s @var{submatcher}. @var{post-match-form} might be used | |
2062 | to move, before resuming with @var{anchored}'s parent's @var{matcher}. | |
2063 | ||
2064 | For example, an element of the form highlights (if not already highlighted): | |
2065 | ||
2066 | @example | |
2067 | ("\\<anchor\\>" (0 anchor-face) ("\\<item\\>" nil nil (0 item-face))) | |
2068 | @end example | |
2069 | ||
2070 | Discrete occurrences of @samp{anchor} in the value of | |
2071 | @code{anchor-face}, and subsequent discrete occurrences of @samp{item} | |
2072 | (on the same line) in the value of @code{item-face}. (Here | |
2073 | @var{pre-match-form} and @var{post-match-form} are @code{nil}. | |
2074 | Therefore @samp{item} is initially searched for starting from the end of | |
2075 | the match of @samp{anchor}, and searching for subsequent instance of | |
2076 | @samp{anchor} resumes from where searching for @samp{item} concluded.) | |
2077 | ||
2078 | The above-mentioned exception is as follows. The limit of the | |
2079 | @var{submatcher} search defaults to the end of the line after | |
2080 | @var{pre-match-form} is evaluated. However, if @var{pre-match-form} | |
2081 | returns a position greater than the position after @var{pre-match-form} | |
2082 | is evaluated, that position is used as the limit of the search. It is | |
2083 | generally a bad idea to return a position greater than the end of the | |
2084 | line; in other words, the @var{submatcher} search should not span lines. | |
2085 | ||
2086 | @item (@var{matcher} @var{highlighters-or-anchoreds} ...) | |
2087 | @end ignore | |
2088 | ||
2089 | @item (eval . @var{form}) | |
969fe9b5 | 2090 | Here @var{form} is an expression to be evaluated the first time |
f9f59935 | 2091 | this value of @code{font-lock-keywords} is used in a buffer. |
969fe9b5 | 2092 | Its value should have one of the forms described in this table. |
f9f59935 RS |
2093 | @end table |
2094 | ||
2095 | @strong{Warning:} Do not design an element of @code{font-lock-keywords} | |
2096 | to match text which spans lines; this does not work reliably. While | |
2097 | @code{font-lock-fontify-buffer} handles multi-line patterns correctly, | |
2098 | updating when you edit the buffer does not, since it considers text one | |
2099 | line at a time. | |
2100 | ||
f9f59935 RS |
2101 | @node Other Font Lock Variables |
2102 | @subsection Other Font Lock Variables | |
2103 | ||
2104 | This section describes additional variables that a major mode | |
2105 | can set by means of @code{font-lock-defaults}. | |
2106 | ||
2107 | @defvar font-lock-keywords-only | |
2108 | Non-@code{nil} means Font Lock should not fontify comments or strings | |
969fe9b5 RS |
2109 | syntactically; it should only fontify based on |
2110 | @code{font-lock-keywords}. | |
f9f59935 RS |
2111 | @end defvar |
2112 | ||
2113 | @ignore | |
a9f0a989 | 2114 | Other variables include those for buffer-specialized fontification functions, |
f9f59935 RS |
2115 | `font-lock-fontify-buffer-function', `font-lock-unfontify-buffer-function', |
2116 | `font-lock-fontify-region-function', `font-lock-unfontify-region-function', | |
2117 | `font-lock-inhibit-thing-lock' and `font-lock-maximum-size'. | |
2118 | @end ignore | |
2119 | ||
2120 | @defvar font-lock-keywords-case-fold-search | |
969fe9b5 RS |
2121 | Non-@code{nil} means that regular expression matching for the sake of |
2122 | @code{font-lock-keywords} should be case-insensitive. | |
f9f59935 RS |
2123 | @end defvar |
2124 | ||
969fe9b5 RS |
2125 | @defvar font-lock-syntax-table |
2126 | This variable specifies the syntax table to use for fontification of | |
2127 | comments and strings. | |
2128 | @end defvar | |
f9f59935 | 2129 | |
969fe9b5 RS |
2130 | @defvar font-lock-beginning-of-syntax-function |
2131 | If this variable is non-@code{nil}, it should be a function to move | |
2132 | point back to a position that is syntactically at ``top level'' and | |
2133 | outside of strings or comments. Font Lock uses this when necessary | |
2134 | to get the right results for syntactic fontification. | |
f9f59935 RS |
2135 | |
2136 | This function is called with no arguments. It should leave point at the | |
2137 | beginning of any enclosing syntactic block. Typical values are | |
2138 | @code{beginning-of-line} (i.e., the start of the line is known to be | |
2139 | outside a syntactic block), or @code{beginning-of-defun} for programming | |
2140 | modes or @code{backward-paragraph} for textual modes (i.e., the | |
2141 | mode-dependent function is known to move outside a syntactic block). | |
2142 | ||
2143 | If the value is @code{nil}, the beginning of the buffer is used as a | |
969fe9b5 RS |
2144 | position outside of a syntactic block. This cannot be wrong, but it can |
2145 | be slow. | |
f9f59935 RS |
2146 | @end defvar |
2147 | ||
2148 | @defvar font-lock-mark-block-function | |
969fe9b5 RS |
2149 | If this variable is non-@code{nil}, it should be a function that is |
2150 | called with no arguments, to choose an enclosing range of text for | |
2151 | refontification for the command @kbd{M-g M-g} | |
2152 | (@code{font-lock-fontify-block}). | |
2153 | ||
2154 | The function should report its choice by placing the region around it. | |
2155 | A good choice is a range of text large enough to give proper results, | |
2156 | but not too large so that refontification becomes slow. Typical values | |
2157 | are @code{mark-defun} for programming modes or @code{mark-paragraph} for | |
2158 | textual modes. | |
f9f59935 RS |
2159 | @end defvar |
2160 | ||
fdba9ef4 | 2161 | @defvar font-lock-extra-managed-props |
bda7c6dd RS |
2162 | Additional properties (other than @code{font-lock-face}) that are |
2163 | being managed by Font Lock mode. Font Lock mode normally manages only | |
2164 | the @code{font-lock-face} property; if you want it to manage others as | |
2165 | well, you must specify them in a @var{facename} in | |
2166 | @code{font-lock-keywords} as well as adding them to this list. | |
fdba9ef4 RS |
2167 | @end defvar |
2168 | ||
f9f59935 RS |
2169 | @node Levels of Font Lock |
2170 | @subsection Levels of Font Lock | |
2171 | ||
2172 | Many major modes offer three different levels of fontification. You | |
2173 | can define multiple levels by using a list of symbols for @var{keywords} | |
2174 | in @code{font-lock-defaults}. Each symbol specifies one level of | |
2175 | fontification; it is up to the user to choose one of these levels. The | |
2176 | chosen level's symbol value is used to initialize | |
2177 | @code{font-lock-keywords}. | |
2178 | ||
969fe9b5 RS |
2179 | Here are the conventions for how to define the levels of |
2180 | fontification: | |
2181 | ||
f9f59935 RS |
2182 | @itemize @bullet |
2183 | @item | |
2184 | Level 1: highlight function declarations, file directives (such as include or | |
2185 | import directives), strings and comments. The idea is speed, so only | |
2186 | the most important and top-level components are fontified. | |
2187 | ||
2188 | @item | |
969fe9b5 RS |
2189 | Level 2: in addition to level 1, highlight all language keywords, |
2190 | including type names that act like keywords, as well as named constant | |
2191 | values. The idea is that all keywords (either syntactic or semantic) | |
2192 | should be fontified appropriately. | |
f9f59935 RS |
2193 | |
2194 | @item | |
969fe9b5 RS |
2195 | Level 3: in addition to level 2, highlight the symbols being defined in |
2196 | function and variable declarations, and all builtin function names, | |
2197 | wherever they appear. | |
f9f59935 RS |
2198 | @end itemize |
2199 | ||
651f7556 CW |
2200 | @node Precalculated Fontification |
2201 | @subsection Precalculated Fontification | |
2202 | ||
2203 | In addition to using @code{font-lock-defaults} for search-based | |
2204 | fontification, you may use the special character property | |
2205 | @code{font-lock-face} (@pxref{Special Properties}). This property | |
2206 | acts just like the explicit @code{face} property, but its activation | |
2207 | is toggled when the user calls @kbd{M-x font-lock-mode}. Using | |
2208 | @code{font-lock-face} is especially conveninent for special modes | |
2209 | which construct their text programmatically, such as | |
2210 | @code{list-buffers} and @code{occur}. | |
2211 | ||
0ab0c481 CW |
2212 | If your mode does not use any of the other machinery of Font Lock |
2213 | (i.e. it only uses the @code{font-lock-face} property), you can tell | |
2214 | Emacs not to load all of font-lock.el (unless it's already loaded), by | |
6fe50867 RS |
2215 | setting the variable @code{font-lock-core-only} to non-@code{nil} as |
2216 | part of the @code{font-lock-defaults} settings. Here is the canonical | |
2217 | way to do this: | |
0ab0c481 CW |
2218 | |
2219 | @example | |
2220 | (set (make-local-variable 'font-lock-defaults) | |
2221 | '(nil t nil nil nil (font-lock-core-only . t))) | |
2222 | @end example | |
2223 | ||
f9f59935 RS |
2224 | @node Faces for Font Lock |
2225 | @subsection Faces for Font Lock | |
2226 | ||
2227 | You can make Font Lock mode use any face, but several faces are | |
2228 | defined specifically for Font Lock mode. Each of these symbols is both | |
2229 | a face name, and a variable whose default value is the symbol itself. | |
2230 | Thus, the default value of @code{font-lock-comment-face} is | |
2231 | @code{font-lock-comment-face}. This means you can write | |
2232 | @code{font-lock-comment-face} in a context such as | |
2233 | @code{font-lock-keywords} where a face-name-valued expression is used. | |
2234 | ||
2235 | @table @code | |
2236 | @item font-lock-comment-face | |
2237 | @vindex font-lock-comment-face | |
f9f59935 RS |
2238 | Used (typically) for comments. |
2239 | ||
2240 | @item font-lock-string-face | |
2241 | @vindex font-lock-string-face | |
f9f59935 RS |
2242 | Used (typically) for string constants. |
2243 | ||
2244 | @item font-lock-keyword-face | |
2245 | @vindex font-lock-keyword-face | |
f9f59935 RS |
2246 | Used (typically) for keywords---names that have special syntactic |
2247 | significance, like @code{for} and @code{if} in C. | |
2248 | ||
2249 | @item font-lock-builtin-face | |
2250 | @vindex font-lock-builtin-face | |
f9f59935 RS |
2251 | Used (typically) for built-in function names. |
2252 | ||
2253 | @item font-lock-function-name-face | |
2254 | @vindex font-lock-function-name-face | |
f9f59935 | 2255 | Used (typically) for the name of a function being defined or declared, |
177c0ea7 | 2256 | in a function definition or declaration. |
f9f59935 RS |
2257 | |
2258 | @item font-lock-variable-name-face | |
2259 | @vindex font-lock-variable-name-face | |
f9f59935 RS |
2260 | Used (typically) for the name of a variable being defined or declared, |
2261 | in a variable definition or declaration. | |
2262 | ||
2263 | @item font-lock-type-face | |
2264 | @vindex font-lock-type-face | |
f9f59935 RS |
2265 | Used (typically) for names of user-defined data types, |
2266 | where they are defined and where they are used. | |
2267 | ||
2268 | @item font-lock-constant-face | |
2269 | @vindex font-lock-constant-face | |
f9f59935 RS |
2270 | Used (typically) for constant names. |
2271 | ||
fdba9ef4 RS |
2272 | @item font-locl-preprocessor-face |
2273 | @vindex font-locl-preprocessor-face | |
2274 | Used (typically) for preprocessor commands. | |
2275 | ||
f9f59935 RS |
2276 | @item font-lock-warning-face |
2277 | @vindex font-lock-warning-face | |
f9f59935 RS |
2278 | Used (typically) for constructs that are peculiar, or that greatly |
2279 | change the meaning of other text. For example, this is used for | |
2280 | @samp{;;;###autoload} cookies in Emacs Lisp, and for @code{#error} | |
2281 | directives in C. | |
2282 | @end table | |
2283 | ||
969fe9b5 RS |
2284 | @node Syntactic Font Lock |
2285 | @subsection Syntactic Font Lock | |
2286 | ||
2287 | Font Lock mode can be used to update @code{syntax-table} properties | |
2288 | automatically. This is useful in languages for which a single syntax | |
2289 | table by itself is not sufficient. | |
2290 | ||
2291 | @defvar font-lock-syntactic-keywords | |
f8cecb20 DL |
2292 | This variable enables and controls syntactic Font Lock. It is |
2293 | normally set via @code{font-lock-defaults}. Its value should be a | |
2294 | list of elements of this form: | |
969fe9b5 RS |
2295 | |
2296 | @example | |
2297 | (@var{matcher} @var{subexp} @var{syntax} @var{override} @var{laxmatch}) | |
2298 | @end example | |
2299 | ||
2300 | The parts of this element have the same meanings as in the corresponding | |
2301 | sort of element of @code{font-lock-keywords}, | |
2302 | ||
2303 | @example | |
2304 | (@var{matcher} @var{subexp} @var{facename} @var{override} @var{laxmatch}) | |
2305 | @end example | |
2306 | ||
2307 | However, instead of specifying the value @var{facename} to use for the | |
f8cecb20 DL |
2308 | @code{face} property, it specifies the value @var{syntax} to use for |
2309 | the @code{syntax-table} property. Here, @var{syntax} can be a string | |
2310 | (as taken by @code{modify-syntax-entry}), a syntax table, a cons cell | |
2311 | (as returned by @code{string-to-syntax}), or an expression whose value | |
2312 | is one of those two types. @var{override} cannot be @code{prepend} or | |
2313 | @code{append}. | |
2314 | ||
2315 | For example, an element of the form: | |
2316 | ||
2317 | @example | |
2318 | ("\\$\\(#\\)" 1 ".") | |
2319 | @end example | |
2320 | ||
2321 | highlights syntactically a hash character when following a dollar | |
2322 | character, with a SYNTAX of @code{"."} (meaning punctuation syntax). | |
2323 | Assuming that the buffer syntax table specifies hash characters to | |
2324 | have comment start syntax, the element will only highlight hash | |
2325 | characters that do not follow dollar characters as comments | |
2326 | syntactically. | |
2327 | ||
2328 | An element of the form: | |
2329 | ||
2330 | @example | |
2331 | ("\\('\\).\\('\\)" | |
2332 | (1 "\"") | |
2333 | (2 "\"")) | |
2334 | @end example | |
2335 | ||
2336 | highlights syntactically both single quotes which surround a single | |
2337 | character, with a SYNTAX of @code{"\""} (meaning string quote syntax). | |
2338 | Assuming that the buffer syntax table does not specify single quotes | |
2339 | to have quote syntax, the element will only highlight single quotes of | |
2340 | the form @samp{'@var{c}'} as strings syntactically. Other forms, such | |
2341 | as @samp{foo'bar} or @samp{'fubar'}, will not be highlighted as | |
2342 | strings. | |
2343 | ||
969fe9b5 RS |
2344 | @end defvar |
2345 | ||
a44af9f2 RS |
2346 | @node Hooks |
2347 | @section Hooks | |
2348 | @cindex hooks | |
2349 | ||
2350 | A @dfn{hook} is a variable where you can store a function or functions | |
2351 | to be called on a particular occasion by an existing program. Emacs | |
2352 | provides hooks for the sake of customization. Most often, hooks are set | |
a40d4712 | 2353 | up in the init file (@pxref{Init File}), but Lisp programs can set them also. |
a44af9f2 RS |
2354 | @xref{Standard Hooks}, for a list of standard hook variables. |
2355 | ||
f9f59935 | 2356 | @cindex normal hook |
a44af9f2 | 2357 | Most of the hooks in Emacs are @dfn{normal hooks}. These variables |
dd73b091 RS |
2358 | contain lists of functions to be called with no arguments. When the |
2359 | hook name ends in @samp{-hook}, that tells you it is normal. We try to | |
2360 | make all hooks normal, as much as possible, so that you can use them in | |
2361 | a uniform way. | |
2362 | ||
2363 | Every major mode function is supposed to run a normal hook called the | |
2364 | @dfn{mode hook} as the last step of initialization. This makes it easy | |
2365 | for a user to customize the behavior of the mode, by overriding the | |
969fe9b5 RS |
2366 | buffer-local variable assignments already made by the mode. But hooks |
2367 | are used in other contexts too. For example, the hook | |
2368 | @code{suspend-hook} runs just before Emacs suspends itself | |
2369 | (@pxref{Suspending Emacs}). | |
a44af9f2 RS |
2370 | |
2371 | The recommended way to add a hook function to a normal hook is by | |
2372 | calling @code{add-hook} (see below). The hook functions may be any of | |
2373 | the valid kinds of functions that @code{funcall} accepts (@pxref{What Is | |
2374 | a Function}). Most normal hook variables are initially void; | |
2375 | @code{add-hook} knows how to deal with this. | |
2376 | ||
f9f59935 | 2377 | @cindex abnormal hook |
dd73b091 | 2378 | If the hook variable's name does not end with @samp{-hook}, that |
a40d4712 | 2379 | indicates it is probably an @dfn{abnormal hook}. Then you should look at its |
dd73b091 RS |
2380 | documentation to see how to use the hook properly. |
2381 | ||
2382 | If the variable's name ends in @samp{-functions} or @samp{-hooks}, | |
2383 | then the value is a list of functions, but it is abnormal in that either | |
2384 | these functions are called with arguments or their values are used in | |
2385 | some way. You can use @code{add-hook} to add a function to the list, | |
2386 | but you must take care in writing the function. (A few of these | |
89cda0c5 SM |
2387 | variables, notably those ending in @samp{-hooks}, are actually |
2388 | normal hooks which were named before we established the convention of | |
2389 | using @samp{-hook} for them.) | |
dd73b091 RS |
2390 | |
2391 | If the variable's name ends in @samp{-function}, then its value | |
2392 | is just a single function, not a list of functions. | |
a44af9f2 | 2393 | |
969fe9b5 RS |
2394 | Here's an example that uses a mode hook to turn on Auto Fill mode when |
2395 | in Lisp Interaction mode: | |
a44af9f2 RS |
2396 | |
2397 | @example | |
2398 | (add-hook 'lisp-interaction-mode-hook 'turn-on-auto-fill) | |
a44af9f2 RS |
2399 | @end example |
2400 | ||
2401 | At the appropriate time, Emacs uses the @code{run-hooks} function to | |
bfe721d1 KH |
2402 | run particular hooks. This function calls the hook functions that have |
2403 | been added with @code{add-hook}. | |
a44af9f2 | 2404 | |
a40d4712 | 2405 | @defun run-hooks &rest hookvars |
a44af9f2 | 2406 | This function takes one or more hook variable names as arguments, and |
a40d4712 PR |
2407 | runs each hook in turn. Each argument should be a symbol that is a hook |
2408 | variable. These arguments are processed in the order specified. | |
a44af9f2 RS |
2409 | |
2410 | If a hook variable has a non-@code{nil} value, that value may be a | |
2411 | function or a list of functions. If the value is a function (either a | |
f9f59935 RS |
2412 | lambda expression or a symbol with a function definition), it is called. |
2413 | If it is a list, the elements are called, in order. The hook functions | |
2414 | are called with no arguments. Nowadays, storing a single function in | |
2415 | the hook variable is semi-obsolete; you should always use a list of | |
2416 | functions. | |
a44af9f2 | 2417 | |
bfe721d1 | 2418 | For example, here's how @code{emacs-lisp-mode} runs its mode hook: |
a44af9f2 RS |
2419 | |
2420 | @example | |
2421 | (run-hooks 'emacs-lisp-mode-hook) | |
2422 | @end example | |
2423 | @end defun | |
2424 | ||
fdba9ef4 RS |
2425 | @defun run-mode-hooks &rest hookvars |
2426 | Like @code{run-hooks}, but is affected by the @code{delay-mode-hooks} | |
2427 | macro. | |
2428 | @end defun | |
2429 | ||
2430 | @defmac delay-mode-hooks body... | |
2431 | This macro executes the @var{body} forms but defers all calls to | |
2432 | @code{run-mode-hooks} within them until the end of @var{body}. | |
2433 | This macro enables a derived mode to arrange not to run | |
2434 | its parent modes' mode hooks until the end. | |
2435 | @end defmac | |
2436 | ||
a9f0a989 RS |
2437 | @defun run-hook-with-args hook &rest args |
2438 | This function is the way to run an abnormal hook which passes arguments | |
2439 | to the hook functions. It calls each of the hook functions, passing | |
2440 | each of them the arguments @var{args}. | |
2441 | @end defun | |
2442 | ||
2443 | @defun run-hook-with-args-until-failure hook &rest args | |
2444 | This function is the way to run an abnormal hook which passes arguments | |
2445 | to the hook functions, and stops as soon as any hook function fails. It | |
2446 | calls each of the hook functions, passing each of them the arguments | |
1911e6e5 | 2447 | @var{args}, until some hook function returns @code{nil}. Then it stops, |
a40d4712 PR |
2448 | and returns @code{nil} if some hook function returned @code{nil}. |
2449 | Otherwise it returns a non-@code{nil} value. | |
a9f0a989 RS |
2450 | @end defun |
2451 | ||
2452 | @defun run-hook-with-args-until-success hook &rest args | |
2453 | This function is the way to run an abnormal hook which passes arguments | |
2454 | to the hook functions, and stops as soon as any hook function succeeds. | |
2455 | It calls each of the hook functions, passing each of them the arguments | |
2456 | @var{args}, until some hook function returns non-@code{nil}. Then it | |
1911e6e5 RS |
2457 | stops, and returns whatever was returned by the last hook function |
2458 | that was called. | |
a9f0a989 RS |
2459 | @end defun |
2460 | ||
22697dac | 2461 | @defun add-hook hook function &optional append local |
a44af9f2 | 2462 | This function is the handy way to add function @var{function} to hook |
de9f0bd9 RS |
2463 | variable @var{hook}. The argument @var{function} may be any valid Lisp |
2464 | function with the proper number of arguments. For example, | |
a44af9f2 RS |
2465 | |
2466 | @example | |
2467 | (add-hook 'text-mode-hook 'my-text-hook-function) | |
2468 | @end example | |
2469 | ||
2470 | @noindent | |
2471 | adds @code{my-text-hook-function} to the hook called @code{text-mode-hook}. | |
2472 | ||
de9f0bd9 RS |
2473 | You can use @code{add-hook} for abnormal hooks as well as for normal |
2474 | hooks. | |
2475 | ||
a44af9f2 RS |
2476 | It is best to design your hook functions so that the order in which they |
2477 | are executed does not matter. Any dependence on the order is ``asking | |
2478 | for trouble.'' However, the order is predictable: normally, | |
2479 | @var{function} goes at the front of the hook list, so it will be | |
969fe9b5 RS |
2480 | executed first (barring another @code{add-hook} call). If the optional |
2481 | argument @var{append} is non-@code{nil}, the new hook function goes at | |
2482 | the end of the hook list and will be executed last. | |
22697dac | 2483 | |
89cda0c5 SM |
2484 | If @var{local} is non-@code{nil}, that says to add @var{function} |
2485 | to the buffer-local hook list instead of to the global hook list. | |
a44af9f2 RS |
2486 | @end defun |
2487 | ||
22697dac | 2488 | @defun remove-hook hook function &optional local |
a44af9f2 | 2489 | This function removes @var{function} from the hook variable @var{hook}. |
c44d2ced | 2490 | |
22697dac | 2491 | If @var{local} is non-@code{nil}, that says to remove @var{function} |
969fe9b5 | 2492 | from the buffer-local hook list instead of from the global hook list. |
22697dac | 2493 | @end defun |
ab5796a9 MB |
2494 | |
2495 | @ignore | |
2496 | arch-tag: 4c7bff41-36e6-4da6-9e7f-9b9289e27c8e | |
2497 | @end ignore |