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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2001, | |
57ebf0be | 4 | @c 2002, 2003, 2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc. |
b8d4c8d0 | 5 | @c See the file elisp.texi for copying conditions. |
6336d8c3 | 6 | @setfilename ../../info/modes |
b8d4c8d0 GM |
7 | @node Modes, Documentation, Keymaps, Top |
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 | * Hooks:: How to use hooks; how to write code that provides hooks. | |
24 | * Major Modes:: Defining major modes. | |
25 | * Minor Modes:: Defining minor modes. | |
26 | * Mode Line Format:: Customizing the text that appears in the mode line. | |
27 | * Imenu:: How a mode can provide a menu | |
28 | of definitions in the buffer. | |
29 | * Font Lock Mode:: How modes can highlight text according to syntax. | |
30 | * Desktop Save Mode:: How modes can have buffer state saved between | |
31 | Emacs sessions. | |
32 | @end menu | |
33 | ||
34 | @node Hooks | |
35 | @section Hooks | |
36 | @cindex hooks | |
37 | ||
38 | A @dfn{hook} is a variable where you can store a function or functions | |
39 | to be called on a particular occasion by an existing program. Emacs | |
40 | provides hooks for the sake of customization. Most often, hooks are set | |
41 | up in the init file (@pxref{Init File}), but Lisp programs can set them also. | |
42 | @xref{Standard Hooks}, for a list of standard hook variables. | |
43 | ||
44 | @cindex normal hook | |
45 | Most of the hooks in Emacs are @dfn{normal hooks}. These variables | |
46 | contain lists of functions to be called with no arguments. By | |
47 | convention, whenever the hook name ends in @samp{-hook}, that tells | |
48 | you it is normal. We try to make all hooks normal, as much as | |
49 | possible, so that you can use them in a uniform way. | |
50 | ||
51 | Every major mode function is supposed to run a normal hook called | |
52 | the @dfn{mode hook} as the one of the last steps of initialization. | |
53 | This makes it easy for a user to customize the behavior of the mode, | |
54 | by overriding the buffer-local variable assignments already made by | |
55 | the mode. Most minor mode functions also run a mode hook at the end. | |
56 | But hooks are used in other contexts too. For example, the hook | |
57 | @code{suspend-hook} runs just before Emacs suspends itself | |
58 | (@pxref{Suspending Emacs}). | |
59 | ||
60 | The recommended way to add a hook function to a normal hook is by | |
61 | calling @code{add-hook} (see below). The hook functions may be any of | |
62 | the valid kinds of functions that @code{funcall} accepts (@pxref{What | |
63 | Is a Function}). Most normal hook variables are initially void; | |
64 | @code{add-hook} knows how to deal with this. You can add hooks either | |
65 | globally or buffer-locally with @code{add-hook}. | |
66 | ||
67 | @cindex abnormal hook | |
68 | If the hook variable's name does not end with @samp{-hook}, that | |
69 | indicates it is probably an @dfn{abnormal hook}. That means the hook | |
70 | functions are called with arguments, or their return values are used | |
71 | in some way. The hook's documentation says how the functions are | |
72 | called. You can use @code{add-hook} to add a function to an abnormal | |
73 | hook, but you must write the function to follow the hook's calling | |
74 | convention. | |
75 | ||
76 | By convention, abnormal hook names end in @samp{-functions} or | |
77 | @samp{-hooks}. If the variable's name ends in @samp{-function}, then | |
78 | its value is just a single function, not a list of functions. | |
79 | ||
fd9a7a58 RS |
80 | @menu |
81 | * Running Hooks:: How to run a hook. | |
82 | * Setting Hooks:: How to put functions on a hook, or remove them. | |
83 | @end menu | |
b8d4c8d0 | 84 | |
fd9a7a58 RS |
85 | @node Running Hooks |
86 | @subsection Running Hooks | |
b8d4c8d0 | 87 | |
fd9a7a58 RS |
88 | At the appropriate times, Emacs uses the @code{run-hooks} function |
89 | and the other functions below to run particular hooks. | |
b8d4c8d0 GM |
90 | |
91 | @defun run-hooks &rest hookvars | |
92 | This function takes one or more normal hook variable names as | |
93 | arguments, and runs each hook in turn. Each argument should be a | |
94 | symbol that is a normal hook variable. These arguments are processed | |
95 | in the order specified. | |
96 | ||
97 | If a hook variable has a non-@code{nil} value, that value should be a | |
98 | list of functions. @code{run-hooks} calls all the functions, one by | |
99 | one, with no arguments. | |
100 | ||
101 | The hook variable's value can also be a single function---either a | |
102 | lambda expression or a symbol with a function definition---which | |
103 | @code{run-hooks} calls. But this usage is obsolete. | |
104 | @end defun | |
105 | ||
106 | @defun run-hook-with-args hook &rest args | |
107 | This function is the way to run an abnormal hook and always call all | |
108 | of the hook functions. It calls each of the hook functions one by | |
109 | one, passing each of them the arguments @var{args}. | |
110 | @end defun | |
111 | ||
112 | @defun run-hook-with-args-until-failure hook &rest args | |
113 | This function is the way to run an abnormal hook until one of the hook | |
114 | functions fails. It calls each of the hook functions, passing each of | |
115 | them the arguments @var{args}, until some hook function returns | |
116 | @code{nil}. It then stops and returns @code{nil}. If none of the | |
117 | hook functions return @code{nil}, it returns a non-@code{nil} value. | |
118 | @end defun | |
119 | ||
120 | @defun run-hook-with-args-until-success hook &rest args | |
121 | This function is the way to run an abnormal hook until a hook function | |
122 | succeeds. It calls each of the hook functions, passing each of them | |
123 | the arguments @var{args}, until some hook function returns | |
124 | non-@code{nil}. Then it stops, and returns whatever was returned by | |
125 | the last hook function that was called. If all hook functions return | |
126 | @code{nil}, it returns @code{nil} as well. | |
127 | @end defun | |
128 | ||
fd9a7a58 RS |
129 | @node Setting Hooks |
130 | @subsection Setting Hooks | |
131 | ||
132 | Here's an example that uses a mode hook to turn on Auto Fill mode when | |
133 | in Lisp Interaction mode: | |
134 | ||
135 | @example | |
136 | (add-hook 'lisp-interaction-mode-hook 'turn-on-auto-fill) | |
137 | @end example | |
138 | ||
b8d4c8d0 GM |
139 | @defun add-hook hook function &optional append local |
140 | This function is the handy way to add function @var{function} to hook | |
141 | variable @var{hook}. You can use it for abnormal hooks as well as for | |
142 | normal hooks. @var{function} can be any Lisp function that can accept | |
143 | the proper number of arguments for @var{hook}. For example, | |
144 | ||
145 | @example | |
146 | (add-hook 'text-mode-hook 'my-text-hook-function) | |
147 | @end example | |
148 | ||
149 | @noindent | |
150 | adds @code{my-text-hook-function} to the hook called @code{text-mode-hook}. | |
151 | ||
152 | If @var{function} is already present in @var{hook} (comparing using | |
153 | @code{equal}), then @code{add-hook} does not add it a second time. | |
154 | ||
fd9a7a58 RS |
155 | If @var{function} has a non-@code{nil} property |
156 | @code{permanent-local-hook}, then @code{kill-all-local-variables} (or | |
157 | changing major modes) won't delete it from the hook variable's local | |
158 | value. | |
159 | ||
b8d4c8d0 GM |
160 | It is best to design your hook functions so that the order in which they |
161 | are executed does not matter. Any dependence on the order is ``asking | |
162 | for trouble.'' However, the order is predictable: normally, | |
163 | @var{function} goes at the front of the hook list, so it will be | |
164 | executed first (barring another @code{add-hook} call). If the optional | |
165 | argument @var{append} is non-@code{nil}, the new hook function goes at | |
166 | the end of the hook list and will be executed last. | |
167 | ||
168 | @code{add-hook} can handle the cases where @var{hook} is void or its | |
169 | value is a single function; it sets or changes the value to a list of | |
170 | functions. | |
171 | ||
172 | If @var{local} is non-@code{nil}, that says to add @var{function} to | |
173 | the buffer-local hook list instead of to the global hook list. If | |
174 | needed, this makes the hook buffer-local and adds @code{t} to the | |
175 | buffer-local value. The latter acts as a flag to run the hook | |
176 | functions in the default value as well as in the local value. | |
177 | @end defun | |
178 | ||
179 | @defun remove-hook hook function &optional local | |
180 | This function removes @var{function} from the hook variable | |
181 | @var{hook}. It compares @var{function} with elements of @var{hook} | |
182 | using @code{equal}, so it works for both symbols and lambda | |
183 | expressions. | |
184 | ||
185 | If @var{local} is non-@code{nil}, that says to remove @var{function} | |
186 | from the buffer-local hook list instead of from the global hook list. | |
187 | @end defun | |
188 | ||
189 | @node Major Modes | |
190 | @section Major Modes | |
191 | @cindex major mode | |
192 | ||
193 | Major modes specialize Emacs for editing particular kinds of text. | |
194 | Each buffer has only one major mode at a time. For each major mode | |
195 | there is a function to switch to that mode in the current buffer; its | |
196 | name should end in @samp{-mode}. These functions work by setting | |
197 | buffer-local variable bindings and other data associated with the | |
198 | buffer, such as a local keymap. The effect lasts until you switch | |
199 | to another major mode in the same buffer. | |
200 | ||
201 | @menu | |
202 | * Major Mode Basics:: | |
203 | * Major Mode Conventions:: Coding conventions for keymaps, etc. | |
204 | * Auto Major Mode:: How Emacs chooses the major mode automatically. | |
205 | * Mode Help:: Finding out how to use a mode. | |
206 | * Derived Modes:: Defining a new major mode based on another major | |
207 | mode. | |
208 | * Generic Modes:: Defining a simple major mode that supports | |
209 | comment syntax and Font Lock mode. | |
210 | * Mode Hooks:: Hooks run at the end of major mode functions. | |
211 | * Example Major Modes:: Text mode and Lisp modes. | |
212 | @end menu | |
213 | ||
214 | @node Major Mode Basics | |
215 | @subsection Major Mode Basics | |
216 | @cindex Fundamental mode | |
217 | ||
218 | The least specialized major mode is called @dfn{Fundamental mode}. | |
219 | This mode has no mode-specific definitions or variable settings, so each | |
220 | Emacs command behaves in its default manner, and each option is in its | |
221 | default state. All other major modes redefine various keys and options. | |
222 | For example, Lisp Interaction mode provides special key bindings for | |
223 | @kbd{C-j} (@code{eval-print-last-sexp}), @key{TAB} | |
224 | (@code{lisp-indent-line}), and other keys. | |
225 | ||
226 | When you need to write several editing commands to help you perform a | |
227 | specialized editing task, creating a new major mode is usually a good | |
228 | idea. In practice, writing a major mode is easy (in contrast to | |
229 | writing a minor mode, which is often difficult). | |
230 | ||
231 | If the new mode is similar to an old one, it is often unwise to | |
232 | modify the old one to serve two purposes, since it may become harder | |
233 | to use and maintain. Instead, copy and rename an existing major mode | |
234 | definition and alter the copy---or use @code{define-derived-mode} to | |
235 | define a @dfn{derived mode} (@pxref{Derived Modes}). For example, | |
236 | Rmail Edit mode is a major mode that is very similar to Text mode | |
237 | except that it provides two additional commands. Its definition is | |
238 | distinct from that of Text mode, but uses that of Text mode. | |
239 | ||
240 | Even if the new mode is not an obvious derivative of any other mode, | |
241 | it is convenient to use @code{define-derived-mode} with a @code{nil} | |
242 | parent argument, since it automatically enforces the most important | |
243 | coding conventions for you. | |
244 | ||
245 | For a very simple programming language major mode that handles | |
246 | comments and fontification, you can use @code{define-generic-mode}. | |
247 | @xref{Generic Modes}. | |
248 | ||
249 | Rmail Edit mode offers an example of changing the major mode | |
250 | temporarily for a buffer, so it can be edited in a different way (with | |
251 | ordinary Emacs commands rather than Rmail commands). In such cases, the | |
252 | temporary major mode usually provides a command to switch back to the | |
253 | buffer's usual mode (Rmail mode, in this case). You might be tempted to | |
254 | present the temporary redefinitions inside a recursive edit and restore | |
255 | the usual ones when the user exits; but this is a bad idea because it | |
256 | constrains the user's options when it is done in more than one buffer: | |
257 | recursive edits must be exited most-recently-entered first. Using an | |
258 | alternative major mode avoids this limitation. @xref{Recursive | |
259 | Editing}. | |
260 | ||
261 | The standard GNU Emacs Lisp library directory tree contains the code | |
262 | for several major modes, in files such as @file{text-mode.el}, | |
263 | @file{texinfo.el}, @file{lisp-mode.el}, @file{c-mode.el}, and | |
264 | @file{rmail.el}. They are found in various subdirectories of the | |
265 | @file{lisp} directory. You can study these libraries to see how modes | |
266 | are written. Text mode is perhaps the simplest major mode aside from | |
267 | Fundamental mode. Rmail mode is a complicated and specialized mode. | |
268 | ||
269 | @node Major Mode Conventions | |
270 | @subsection Major Mode Conventions | |
271 | @cindex major mode conventions | |
272 | @cindex conventions for writing major modes | |
273 | ||
274 | The code for existing major modes follows various coding conventions, | |
275 | including conventions for local keymap and syntax table initialization, | |
276 | global names, and hooks. Please follow these conventions when you | |
277 | define a new major mode. (Fundamental mode is an exception to many | |
278 | of these conventions, because its definition is to present the global | |
279 | state of Emacs.) | |
280 | ||
281 | This list of conventions is only partial, because each major mode | |
282 | should aim for consistency in general with other Emacs major modes. | |
283 | This makes Emacs as a whole more coherent. It is impossible to list | |
284 | here all the possible points where this issue might come up; if the | |
285 | Emacs developers point out an area where your major mode deviates from | |
286 | the usual conventions, please make it compatible. | |
287 | ||
288 | @itemize @bullet | |
289 | @item | |
290 | Define a command whose name ends in @samp{-mode}, with no arguments, | |
291 | that switches to the new mode in the current buffer. This command | |
292 | should set up the keymap, syntax table, and buffer-local variables in an | |
293 | existing buffer, without changing the buffer's contents. | |
294 | ||
295 | @item | |
296 | Write a documentation string for this command that describes the | |
297 | special commands available in this mode. @kbd{C-h m} | |
298 | (@code{describe-mode}) in your mode will display this string. | |
299 | ||
300 | The documentation string may include the special documentation | |
301 | substrings, @samp{\[@var{command}]}, @samp{\@{@var{keymap}@}}, and | |
302 | @samp{\<@var{keymap}>}, which enable the documentation to adapt | |
303 | automatically to the user's own key bindings. @xref{Keys in | |
304 | Documentation}. | |
305 | ||
306 | @item | |
307 | The major mode command should start by calling | |
308 | @code{kill-all-local-variables}. This runs the normal hook | |
309 | @code{change-major-mode-hook}, then gets rid of the buffer-local | |
310 | variables of the major mode previously in effect. @xref{Creating | |
311 | Buffer-Local}. | |
312 | ||
313 | @item | |
314 | The major mode command should set the variable @code{major-mode} to the | |
315 | major mode command symbol. This is how @code{describe-mode} discovers | |
316 | which documentation to print. | |
317 | ||
318 | @item | |
319 | The major mode command should set the variable @code{mode-name} to the | |
9cf52b11 EZ |
320 | ``pretty'' name of the mode, usually a string (but see @ref{Mode Line |
321 | Data}, for other possible forms). The name of the mode appears | |
322 | in the mode line. | |
b8d4c8d0 GM |
323 | |
324 | @item | |
325 | @cindex functions in modes | |
326 | Since all global names are in the same name space, all the global | |
327 | variables, constants, and functions that are part of the mode should | |
328 | have names that start with the major mode name (or with an abbreviation | |
329 | of it if the name is long). @xref{Coding Conventions}. | |
330 | ||
331 | @item | |
332 | In a major mode for editing some kind of structured text, such as a | |
333 | programming language, indentation of text according to structure is | |
334 | probably useful. So the mode should set @code{indent-line-function} | |
335 | to a suitable function, and probably customize other variables | |
336 | for indentation. | |
337 | ||
338 | @item | |
339 | @cindex keymaps in modes | |
340 | The major mode should usually have its own keymap, which is used as the | |
341 | local keymap in all buffers in that mode. The major mode command should | |
342 | call @code{use-local-map} to install this local map. @xref{Active | |
343 | Keymaps}, for more information. | |
344 | ||
345 | This keymap should be stored permanently in a global variable named | |
346 | @code{@var{modename}-mode-map}. Normally the library that defines the | |
347 | mode sets this variable. | |
348 | ||
349 | @xref{Tips for Defining}, for advice about how to write the code to set | |
350 | up the mode's keymap variable. | |
351 | ||
352 | @item | |
353 | The key sequences bound in a major mode keymap should usually start with | |
354 | @kbd{C-c}, followed by a control character, a digit, or @kbd{@{}, | |
355 | @kbd{@}}, @kbd{<}, @kbd{>}, @kbd{:} or @kbd{;}. The other punctuation | |
356 | characters are reserved for minor modes, and ordinary letters are | |
357 | reserved for users. | |
358 | ||
359 | A major mode can also rebind the keys @kbd{M-n}, @kbd{M-p} and | |
360 | @kbd{M-s}. The bindings for @kbd{M-n} and @kbd{M-p} should normally | |
361 | be some kind of ``moving forward and backward,'' but this does not | |
362 | necessarily mean cursor motion. | |
363 | ||
364 | It is legitimate for a major mode to rebind a standard key sequence if | |
365 | it provides a command that does ``the same job'' in a way better | |
366 | suited to the text this mode is used for. For example, a major mode | |
367 | for editing a programming language might redefine @kbd{C-M-a} to | |
368 | ``move to the beginning of a function'' in a way that works better for | |
369 | that language. | |
370 | ||
371 | It is also legitimate for a major mode to rebind a standard key | |
372 | sequence whose standard meaning is rarely useful in that mode. For | |
373 | instance, minibuffer modes rebind @kbd{M-r}, whose standard meaning is | |
374 | rarely of any use in the minibuffer. Major modes such as Dired or | |
375 | Rmail that do not allow self-insertion of text can reasonably redefine | |
376 | letters and other printing characters as special commands. | |
377 | ||
378 | @item | |
379 | Major modes modes for editing text should not define @key{RET} to do | |
380 | anything other than insert a newline. However, it is ok for | |
381 | specialized modes for text that users don't directly edit, such as | |
382 | Dired and Info modes, to redefine @key{RET} to do something entirely | |
383 | different. | |
384 | ||
385 | @item | |
386 | Major modes should not alter options that are primarily a matter of user | |
387 | preference, such as whether Auto-Fill mode is enabled. Leave this to | |
388 | each user to decide. However, a major mode should customize other | |
389 | variables so that Auto-Fill mode will work usefully @emph{if} the user | |
390 | decides to use it. | |
391 | ||
392 | @item | |
393 | @cindex syntax tables in modes | |
394 | The mode may have its own syntax table or may share one with other | |
395 | related modes. If it has its own syntax table, it should store this in | |
396 | a variable named @code{@var{modename}-mode-syntax-table}. @xref{Syntax | |
397 | Tables}. | |
398 | ||
399 | @item | |
400 | If the mode handles a language that has a syntax for comments, it should | |
401 | set the variables that define the comment syntax. @xref{Options for | |
402 | Comments,, Options Controlling Comments, emacs, The GNU Emacs Manual}. | |
403 | ||
404 | @item | |
405 | @cindex abbrev tables in modes | |
406 | The mode may have its own abbrev table or may share one with other | |
407 | related modes. If it has its own abbrev table, it should store this | |
408 | in a variable named @code{@var{modename}-mode-abbrev-table}. If the | |
409 | major mode command defines any abbrevs itself, it should pass @code{t} | |
410 | for the @var{system-flag} argument to @code{define-abbrev}. | |
411 | @xref{Defining Abbrevs}. | |
412 | ||
413 | @item | |
414 | The mode should specify how to do highlighting for Font Lock mode, by | |
415 | setting up a buffer-local value for the variable | |
416 | @code{font-lock-defaults} (@pxref{Font Lock Mode}). | |
417 | ||
418 | @item | |
419 | The mode should specify how Imenu should find the definitions or | |
420 | sections of a buffer, by setting up a buffer-local value for the | |
421 | variable @code{imenu-generic-expression}, for the two variables | |
422 | @code{imenu-prev-index-position-function} and | |
423 | @code{imenu-extract-index-name-function}, or for the variable | |
424 | @code{imenu-create-index-function} (@pxref{Imenu}). | |
425 | ||
426 | @item | |
427 | The mode can specify a local value for | |
428 | @code{eldoc-documentation-function} to tell ElDoc mode how to handle | |
429 | this mode. | |
430 | ||
431 | @item | |
432 | Use @code{defvar} or @code{defcustom} to set mode-related variables, so | |
433 | that they are not reinitialized if they already have a value. (Such | |
434 | reinitialization could discard customizations made by the user.) | |
435 | ||
436 | @item | |
437 | @cindex buffer-local variables in modes | |
438 | To make a buffer-local binding for an Emacs customization variable, use | |
439 | @code{make-local-variable} in the major mode command, not | |
440 | @code{make-variable-buffer-local}. The latter function would make the | |
441 | variable local to every buffer in which it is subsequently set, which | |
442 | would affect buffers that do not use this mode. It is undesirable for a | |
443 | mode to have such global effects. @xref{Buffer-Local Variables}. | |
444 | ||
445 | With rare exceptions, the only reasonable way to use | |
446 | @code{make-variable-buffer-local} in a Lisp package is for a variable | |
447 | which is used only within that package. Using it on a variable used by | |
448 | other packages would interfere with them. | |
449 | ||
450 | @item | |
451 | @cindex mode hook | |
452 | @cindex major mode hook | |
453 | Each major mode should have a normal @dfn{mode hook} named | |
454 | @code{@var{modename}-mode-hook}. The very last thing the major mode command | |
455 | should do is to call @code{run-mode-hooks}. This runs the mode hook, | |
456 | and then runs the normal hook @code{after-change-major-mode-hook}. | |
457 | @xref{Mode Hooks}. | |
458 | ||
459 | @item | |
460 | The major mode command may start by calling some other major mode | |
461 | command (called the @dfn{parent mode}) and then alter some of its | |
462 | settings. A mode that does this is called a @dfn{derived mode}. The | |
463 | recommended way to define one is to use @code{define-derived-mode}, | |
464 | but this is not required. Such a mode should call the parent mode | |
465 | command inside a @code{delay-mode-hooks} form. (Using | |
466 | @code{define-derived-mode} does this automatically.) @xref{Derived | |
467 | Modes}, and @ref{Mode Hooks}. | |
468 | ||
469 | @item | |
470 | If something special should be done if the user switches a buffer from | |
471 | this mode to any other major mode, this mode can set up a buffer-local | |
472 | value for @code{change-major-mode-hook} (@pxref{Creating Buffer-Local}). | |
473 | ||
474 | @item | |
475 | If this mode is appropriate only for specially-prepared text, then the | |
476 | major mode command symbol should have a property named @code{mode-class} | |
477 | with value @code{special}, put on as follows: | |
478 | ||
479 | @kindex mode-class @r{(property)} | |
480 | @cindex @code{special} | |
481 | @example | |
482 | (put 'funny-mode 'mode-class 'special) | |
483 | @end example | |
484 | ||
485 | @noindent | |
486 | This tells Emacs that new buffers created while the current buffer is | |
487 | in Funny mode should not inherit Funny mode, in case | |
488 | @code{default-major-mode} is @code{nil}. Modes such as Dired, Rmail, | |
489 | and Buffer List use this feature. | |
490 | ||
491 | @item | |
492 | If you want to make the new mode the default for files with certain | |
493 | recognizable names, add an element to @code{auto-mode-alist} to select | |
494 | the mode for those file names (@pxref{Auto Major Mode}). If you | |
495 | define the mode command to autoload, you should add this element in | |
496 | the same file that calls @code{autoload}. If you use an autoload | |
497 | cookie for the mode command, you can also use an autoload cookie for | |
498 | the form that adds the element (@pxref{autoload cookie}). If you do | |
499 | not autoload the mode command, it is sufficient to add the element in | |
500 | the file that contains the mode definition. | |
501 | ||
502 | @item | |
503 | In the comments that document the file, you should provide a sample | |
504 | @code{autoload} form and an example of how to add to | |
505 | @code{auto-mode-alist}, that users can include in their init files | |
506 | (@pxref{Init File}). | |
507 | ||
508 | @item | |
509 | @cindex mode loading | |
510 | The top-level forms in the file defining the mode should be written so | |
511 | that they may be evaluated more than once without adverse consequences. | |
512 | Even if you never load the file more than once, someone else will. | |
513 | @end itemize | |
514 | ||
515 | @node Auto Major Mode | |
516 | @subsection How Emacs Chooses a Major Mode | |
517 | @cindex major mode, automatic selection | |
518 | ||
519 | Based on information in the file name or in the file itself, Emacs | |
520 | automatically selects a major mode for the new buffer when a file is | |
521 | visited. It also processes local variables specified in the file text. | |
522 | ||
523 | @deffn Command fundamental-mode | |
524 | Fundamental mode is a major mode that is not specialized for anything | |
525 | in particular. Other major modes are defined in effect by comparison | |
526 | with this one---their definitions say what to change, starting from | |
527 | Fundamental mode. The @code{fundamental-mode} function does @emph{not} | |
528 | run any mode hooks; you're not supposed to customize it. (If you want Emacs | |
529 | to behave differently in Fundamental mode, change the @emph{global} | |
530 | state of Emacs.) | |
531 | @end deffn | |
532 | ||
533 | @deffn Command normal-mode &optional find-file | |
534 | This function establishes the proper major mode and buffer-local variable | |
535 | bindings for the current buffer. First it calls @code{set-auto-mode} | |
536 | (see below), then it runs @code{hack-local-variables} to parse, and | |
537 | bind or evaluate as appropriate, the file's local variables | |
538 | (@pxref{File Local Variables}). | |
539 | ||
540 | If the @var{find-file} argument to @code{normal-mode} is non-@code{nil}, | |
541 | @code{normal-mode} assumes that the @code{find-file} function is calling | |
542 | it. In this case, it may process local variables in the @samp{-*-} | |
543 | line or at the end of the file. The variable | |
544 | @code{enable-local-variables} controls whether to do so. @xref{File | |
545 | Variables, , Local Variables in Files, emacs, The GNU Emacs Manual}, | |
546 | for the syntax of the local variables section of a file. | |
547 | ||
548 | If you run @code{normal-mode} interactively, the argument | |
549 | @var{find-file} is normally @code{nil}. In this case, | |
550 | @code{normal-mode} unconditionally processes any file local variables. | |
551 | ||
552 | If @code{normal-mode} processes the local variables list and this list | |
553 | specifies a major mode, that mode overrides any mode chosen by | |
554 | @code{set-auto-mode}. If neither @code{set-auto-mode} nor | |
555 | @code{hack-local-variables} specify a major mode, the buffer stays in | |
556 | the major mode determined by @code{default-major-mode} (see below). | |
557 | ||
558 | @cindex file mode specification error | |
559 | @code{normal-mode} uses @code{condition-case} around the call to the | |
560 | major mode function, so errors are caught and reported as a @samp{File | |
561 | mode specification error}, followed by the original error message. | |
562 | @end deffn | |
563 | ||
564 | @defun set-auto-mode &optional keep-mode-if-same | |
565 | @cindex visited file mode | |
566 | This function selects the major mode that is appropriate for the | |
567 | current buffer. It bases its decision (in order of precedence) on | |
568 | the @w{@samp{-*-}} line, on the @w{@samp{#!}} line (using | |
569 | @code{interpreter-mode-alist}), on the text at the beginning of the | |
570 | buffer (using @code{magic-mode-alist}), and finally on the visited | |
571 | file name (using @code{auto-mode-alist}). @xref{Choosing Modes, , How | |
572 | Major Modes are Chosen, emacs, The GNU Emacs Manual}. However, this | |
573 | function does not look for the @samp{mode:} local variable near the | |
574 | end of a file; the @code{hack-local-variables} function does that. | |
575 | If @code{enable-local-variables} is @code{nil}, @code{set-auto-mode} | |
576 | does not check the @w{@samp{-*-}} line for a mode tag either. | |
577 | ||
578 | If @var{keep-mode-if-same} is non-@code{nil}, this function does not | |
579 | call the mode command if the buffer is already in the proper major | |
580 | mode. For instance, @code{set-visited-file-name} sets this to | |
581 | @code{t} to avoid killing buffer local variables that the user may | |
582 | have set. | |
583 | @end defun | |
584 | ||
585 | @defopt default-major-mode | |
586 | This variable holds the default major mode for new buffers. The | |
587 | standard value is @code{fundamental-mode}. | |
588 | ||
589 | If the value of @code{default-major-mode} is @code{nil}, Emacs uses | |
590 | the (previously) current buffer's major mode as the default major mode | |
591 | of a new buffer. However, if that major mode symbol has a @code{mode-class} | |
592 | property with value @code{special}, then it is not used for new buffers; | |
593 | Fundamental mode is used instead. The modes that have this property are | |
594 | those such as Dired and Rmail that are useful only with text that has | |
595 | been specially prepared. | |
596 | @end defopt | |
597 | ||
598 | @defun set-buffer-major-mode buffer | |
599 | This function sets the major mode of @var{buffer} to the value of | |
600 | @code{default-major-mode}; if that variable is @code{nil}, it uses the | |
601 | current buffer's major mode (if that is suitable). As an exception, | |
602 | if @var{buffer}'s name is @samp{*scratch*}, it sets the mode to | |
603 | @code{initial-major-mode}. | |
604 | ||
605 | The low-level primitives for creating buffers do not use this function, | |
606 | but medium-level commands such as @code{switch-to-buffer} and | |
607 | @code{find-file-noselect} use it whenever they create buffers. | |
608 | @end defun | |
609 | ||
610 | @defopt initial-major-mode | |
611 | @cindex @samp{*scratch*} | |
612 | The value of this variable determines the major mode of the initial | |
613 | @samp{*scratch*} buffer. The value should be a symbol that is a major | |
614 | mode command. The default value is @code{lisp-interaction-mode}. | |
615 | @end defopt | |
616 | ||
617 | @defvar interpreter-mode-alist | |
618 | This variable specifies major modes to use for scripts that specify a | |
619 | command interpreter in a @samp{#!} line. Its value is an alist with | |
620 | elements of the form @code{(@var{interpreter} . @var{mode})}; for | |
621 | example, @code{("perl" . perl-mode)} is one element present by | |
622 | default. The element says to use mode @var{mode} if the file | |
623 | specifies an interpreter which matches @var{interpreter}. | |
624 | @end defvar | |
625 | ||
626 | @defvar magic-mode-alist | |
627 | This variable's value is an alist with elements of the form | |
628 | @code{(@var{regexp} . @var{function})}, where @var{regexp} is a | |
629 | regular expression and @var{function} is a function or @code{nil}. | |
630 | After visiting a file, @code{set-auto-mode} calls @var{function} if | |
631 | the text at the beginning of the buffer matches @var{regexp} and | |
632 | @var{function} is non-@code{nil}; if @var{function} is @code{nil}, | |
633 | @code{auto-mode-alist} gets to decide the mode. | |
634 | @end defvar | |
635 | ||
636 | @defvar magic-fallback-mode-alist | |
637 | This works like @code{magic-mode-alist}, except that it is handled | |
638 | only if @code{auto-mode-alist} does not specify a mode for this file. | |
639 | @end defvar | |
640 | ||
641 | @defvar auto-mode-alist | |
642 | This variable contains an association list of file name patterns | |
643 | (regular expressions) and corresponding major mode commands. Usually, | |
644 | the file name patterns test for suffixes, such as @samp{.el} and | |
645 | @samp{.c}, but this need not be the case. An ordinary element of the | |
646 | alist looks like @code{(@var{regexp} . @var{mode-function})}. | |
647 | ||
648 | For example, | |
649 | ||
650 | @smallexample | |
651 | @group | |
652 | (("\\`/tmp/fol/" . text-mode) | |
653 | ("\\.texinfo\\'" . texinfo-mode) | |
654 | ("\\.texi\\'" . texinfo-mode) | |
655 | @end group | |
656 | @group | |
657 | ("\\.el\\'" . emacs-lisp-mode) | |
658 | ("\\.c\\'" . c-mode) | |
659 | ("\\.h\\'" . c-mode) | |
660 | @dots{}) | |
661 | @end group | |
662 | @end smallexample | |
663 | ||
664 | When you visit a file whose expanded file name (@pxref{File Name | |
665 | Expansion}), with version numbers and backup suffixes removed using | |
666 | @code{file-name-sans-versions} (@pxref{File Name Components}), matches | |
667 | a @var{regexp}, @code{set-auto-mode} calls the corresponding | |
668 | @var{mode-function}. This feature enables Emacs to select the proper | |
669 | major mode for most files. | |
670 | ||
671 | If an element of @code{auto-mode-alist} has the form @code{(@var{regexp} | |
672 | @var{function} t)}, then after calling @var{function}, Emacs searches | |
673 | @code{auto-mode-alist} again for a match against the portion of the file | |
674 | name that did not match before. This feature is useful for | |
675 | uncompression packages: an entry of the form @code{("\\.gz\\'" | |
676 | @var{function} t)} can uncompress the file and then put the uncompressed | |
677 | file in the proper mode according to the name sans @samp{.gz}. | |
678 | ||
679 | Here is an example of how to prepend several pattern pairs to | |
680 | @code{auto-mode-alist}. (You might use this sort of expression in your | |
681 | init file.) | |
682 | ||
683 | @smallexample | |
684 | @group | |
685 | (setq auto-mode-alist | |
686 | (append | |
687 | ;; @r{File name (within directory) starts with a dot.} | |
688 | '(("/\\.[^/]*\\'" . fundamental-mode) | |
689 | ;; @r{File name has no dot.} | |
690 | ("[^\\./]*\\'" . fundamental-mode) | |
691 | ;; @r{File name ends in @samp{.C}.} | |
692 | ("\\.C\\'" . c++-mode)) | |
693 | auto-mode-alist)) | |
694 | @end group | |
695 | @end smallexample | |
696 | @end defvar | |
697 | ||
698 | @node Mode Help | |
699 | @subsection Getting Help about a Major Mode | |
700 | @cindex mode help | |
701 | @cindex help for major mode | |
702 | @cindex documentation for major mode | |
703 | ||
704 | The @code{describe-mode} function is used to provide information | |
705 | about major modes. It is normally called with @kbd{C-h m}. The | |
706 | @code{describe-mode} function uses the value of @code{major-mode}, | |
707 | which is why every major mode function needs to set the | |
708 | @code{major-mode} variable. | |
709 | ||
710 | @deffn Command describe-mode | |
711 | This function displays the documentation of the current major mode. | |
712 | ||
713 | The @code{describe-mode} function calls the @code{documentation} | |
714 | function using the value of @code{major-mode} as an argument. Thus, it | |
715 | displays the documentation string of the major mode function. | |
716 | (@xref{Accessing Documentation}.) | |
717 | @end deffn | |
718 | ||
719 | @defvar major-mode | |
720 | This buffer-local variable holds the symbol for the current buffer's | |
721 | major mode. This symbol should have a function definition that is the | |
722 | command to switch to that major mode. The @code{describe-mode} | |
723 | function uses the documentation string of the function as the | |
724 | documentation of the major mode. | |
725 | @end defvar | |
726 | ||
727 | @node Derived Modes | |
728 | @subsection Defining Derived Modes | |
729 | @cindex derived mode | |
730 | ||
731 | It's often useful to define a new major mode in terms of an existing | |
732 | one. An easy way to do this is to use @code{define-derived-mode}. | |
733 | ||
734 | @defmac define-derived-mode variant parent name docstring keyword-args@dots{} body@dots{} | |
735 | This construct defines @var{variant} as a major mode command, using | |
736 | @var{name} as the string form of the mode name. @var{variant} and | |
737 | @var{parent} should be unquoted symbols. | |
738 | ||
739 | The new command @var{variant} is defined to call the function | |
740 | @var{parent}, then override certain aspects of that parent mode: | |
741 | ||
742 | @itemize @bullet | |
743 | @item | |
744 | The new mode has its own sparse keymap, named | |
745 | @code{@var{variant}-map}. @code{define-derived-mode} | |
746 | makes the parent mode's keymap the parent of the new map, unless | |
747 | @code{@var{variant}-map} is already set and already has a parent. | |
748 | ||
749 | @item | |
750 | The new mode has its own syntax table, kept in the variable | |
751 | @code{@var{variant}-syntax-table}, unless you override this using the | |
752 | @code{:syntax-table} keyword (see below). @code{define-derived-mode} | |
753 | makes the parent mode's syntax-table the parent of | |
754 | @code{@var{variant}-syntax-table}, unless the latter is already set | |
755 | and already has a parent different from the standard syntax table. | |
756 | ||
757 | @item | |
758 | The new mode has its own abbrev table, kept in the variable | |
759 | @code{@var{variant}-abbrev-table}, unless you override this using the | |
760 | @code{:abbrev-table} keyword (see below). | |
761 | ||
762 | @item | |
763 | The new mode has its own mode hook, @code{@var{variant}-hook}. It | |
764 | runs this hook, after running the hooks of its ancestor modes, with | |
765 | @code{run-mode-hooks}, as the last thing it does. @xref{Mode Hooks}. | |
766 | @end itemize | |
767 | ||
768 | In addition, you can specify how to override other aspects of | |
769 | @var{parent} with @var{body}. The command @var{variant} | |
770 | evaluates the forms in @var{body} after setting up all its usual | |
771 | overrides, just before running the mode hooks. | |
772 | ||
773 | You can also specify @code{nil} for @var{parent}. This gives the new | |
774 | mode no parent. Then @code{define-derived-mode} behaves as described | |
775 | above, but, of course, omits all actions connected with @var{parent}. | |
776 | ||
777 | The argument @var{docstring} specifies the documentation string for | |
778 | the new mode. @code{define-derived-mode} adds some general | |
779 | information about the mode's hook, followed by the mode's keymap, at | |
780 | the end of this docstring. If you omit @var{docstring}, | |
781 | @code{define-derived-mode} generates a documentation string. | |
782 | ||
783 | The @var{keyword-args} are pairs of keywords and values. The values | |
784 | are evaluated. The following keywords are currently supported: | |
785 | ||
786 | @table @code | |
787 | @item :syntax-table | |
788 | You can use this to explicitly specify a syntax table for the new | |
789 | mode. If you specify a @code{nil} value, the new mode uses the same | |
790 | syntax table as @var{parent}, or the standard syntax table if | |
791 | @var{parent} is @code{nil}. (Note that this does @emph{not} follow | |
792 | the convention used for non-keyword arguments that a @code{nil} value | |
793 | is equivalent with not specifying the argument.) | |
794 | ||
795 | @item :abbrev-table | |
796 | You can use this to explicitly specify an abbrev table for the new | |
797 | mode. If you specify a @code{nil} value, the new mode uses the same | |
798 | abbrev table as @var{parent}, or @code{fundamental-mode-abbrev-table} | |
799 | if @var{parent} is @code{nil}. (Again, a @code{nil} value is | |
800 | @emph{not} equivalent to not specifying this keyword.) | |
801 | ||
802 | @item :group | |
803 | If this is specified, the value should be the customization group for | |
804 | this mode. (Not all major modes have one.) Only the (still | |
805 | experimental and unadvertised) command @code{customize-mode} currently | |
806 | uses this. @code{define-derived-mode} does @emph{not} automatically | |
807 | define the specified customization group. | |
808 | @end table | |
809 | ||
810 | Here is a hypothetical example: | |
811 | ||
812 | @example | |
813 | (define-derived-mode hypertext-mode | |
814 | text-mode "Hypertext" | |
815 | "Major mode for hypertext. | |
816 | \\@{hypertext-mode-map@}" | |
817 | (setq case-fold-search nil)) | |
818 | ||
819 | (define-key hypertext-mode-map | |
820 | [down-mouse-3] 'do-hyper-link) | |
821 | @end example | |
822 | ||
823 | Do not write an @code{interactive} spec in the definition; | |
824 | @code{define-derived-mode} does that automatically. | |
825 | @end defmac | |
826 | ||
827 | @node Generic Modes | |
828 | @subsection Generic Modes | |
829 | @cindex generic mode | |
830 | ||
831 | @dfn{Generic modes} are simple major modes with basic support for | |
832 | comment syntax and Font Lock mode. To define a generic mode, use the | |
833 | macro @code{define-generic-mode}. See the file @file{generic-x.el} | |
834 | for some examples of the use of @code{define-generic-mode}. | |
835 | ||
836 | @defmac define-generic-mode mode comment-list keyword-list font-lock-list auto-mode-list function-list &optional docstring | |
837 | This macro defines a generic mode command named @var{mode} (a symbol, | |
838 | not quoted). The optional argument @var{docstring} is the | |
839 | documentation for the mode command. If you do not supply it, | |
840 | @code{define-generic-mode} generates one by default. | |
841 | ||
842 | The argument @var{comment-list} is a list in which each element is | |
843 | either a character, a string of one or two characters, or a cons cell. | |
844 | A character or a string is set up in the mode's syntax table as a | |
845 | ``comment starter.'' If the entry is a cons cell, the @sc{car} is set | |
846 | up as a ``comment starter'' and the @sc{cdr} as a ``comment ender.'' | |
847 | (Use @code{nil} for the latter if you want comments to end at the end | |
848 | of the line.) Note that the syntax table mechanism has limitations | |
849 | about what comment starters and enders are actually possible. | |
850 | @xref{Syntax Tables}. | |
851 | ||
852 | The argument @var{keyword-list} is a list of keywords to highlight | |
853 | with @code{font-lock-keyword-face}. Each keyword should be a string. | |
854 | Meanwhile, @var{font-lock-list} is a list of additional expressions to | |
855 | highlight. Each element of this list should have the same form as an | |
856 | element of @code{font-lock-keywords}. @xref{Search-based | |
857 | Fontification}. | |
858 | ||
859 | The argument @var{auto-mode-list} is a list of regular expressions to | |
860 | add to the variable @code{auto-mode-alist}. They are added by the execution | |
861 | of the @code{define-generic-mode} form, not by expanding the macro call. | |
862 | ||
863 | Finally, @var{function-list} is a list of functions for the mode | |
864 | command to call for additional setup. It calls these functions just | |
865 | before it runs the mode hook variable @code{@var{mode}-hook}. | |
866 | @end defmac | |
867 | ||
868 | @node Mode Hooks | |
869 | @subsection Mode Hooks | |
870 | ||
871 | Every major mode function should finish by running its mode hook and | |
872 | the mode-independent normal hook @code{after-change-major-mode-hook}. | |
873 | It does this by calling @code{run-mode-hooks}. If the major mode is a | |
874 | derived mode, that is if it calls another major mode (the parent mode) | |
875 | in its body, it should do this inside @code{delay-mode-hooks} so that | |
876 | the parent won't run these hooks itself. Instead, the derived mode's | |
877 | call to @code{run-mode-hooks} runs the parent's mode hook too. | |
878 | @xref{Major Mode Conventions}. | |
879 | ||
880 | Emacs versions before Emacs 22 did not have @code{delay-mode-hooks}. | |
881 | When user-implemented major modes have not been updated to use it, | |
882 | they won't entirely follow these conventions: they may run the | |
883 | parent's mode hook too early, or fail to run | |
884 | @code{after-change-major-mode-hook}. If you encounter such a major | |
885 | mode, please correct it to follow these conventions. | |
886 | ||
887 | When you defined a major mode using @code{define-derived-mode}, it | |
888 | automatically makes sure these conventions are followed. If you | |
889 | define a major mode ``by hand,'' not using @code{define-derived-mode}, | |
890 | use the following functions to handle these conventions automatically. | |
891 | ||
892 | @defun run-mode-hooks &rest hookvars | |
893 | Major modes should run their mode hook using this function. It is | |
894 | similar to @code{run-hooks} (@pxref{Hooks}), but it also runs | |
895 | @code{after-change-major-mode-hook}. | |
896 | ||
897 | When this function is called during the execution of a | |
898 | @code{delay-mode-hooks} form, it does not run the hooks immediately. | |
899 | Instead, it arranges for the next call to @code{run-mode-hooks} to run | |
900 | them. | |
901 | @end defun | |
902 | ||
903 | @defmac delay-mode-hooks body@dots{} | |
904 | When one major mode command calls another, it should do so inside of | |
905 | @code{delay-mode-hooks}. | |
906 | ||
907 | This macro executes @var{body}, but tells all @code{run-mode-hooks} | |
908 | calls during the execution of @var{body} to delay running their hooks. | |
909 | The hooks will actually run during the next call to | |
910 | @code{run-mode-hooks} after the end of the @code{delay-mode-hooks} | |
911 | construct. | |
912 | @end defmac | |
913 | ||
914 | @defvar after-change-major-mode-hook | |
915 | This is a normal hook run by @code{run-mode-hooks}. It is run at the | |
916 | very end of every properly-written major mode function. | |
917 | @end defvar | |
918 | ||
919 | @node Example Major Modes | |
920 | @subsection Major Mode Examples | |
921 | ||
922 | Text mode is perhaps the simplest mode besides Fundamental mode. | |
923 | Here are excerpts from @file{text-mode.el} that illustrate many of | |
924 | the conventions listed above: | |
925 | ||
926 | @smallexample | |
927 | @group | |
928 | ;; @r{Create the syntax table for this mode.} | |
929 | (defvar text-mode-syntax-table | |
930 | (let ((st (make-syntax-table))) | |
931 | (modify-syntax-entry ?\" ". " st) | |
932 | (modify-syntax-entry ?\\ ". " st) | |
933 | ;; Add `p' so M-c on `hello' leads to `Hello', not `hello'. | |
934 | (modify-syntax-entry ?' "w p" st) | |
935 | st) | |
936 | "Syntax table used while in `text-mode'.") | |
937 | @end group | |
938 | ||
939 | ;; @r{Create the keymap for this mode.} | |
940 | @group | |
941 | (defvar text-mode-map | |
942 | (let ((map (make-sparse-keymap))) | |
943 | (define-key map "\e\t" 'ispell-complete-word) | |
944 | (define-key map "\es" 'center-line) | |
945 | (define-key map "\eS" 'center-paragraph) | |
946 | map) | |
947 | "Keymap for `text-mode'. | |
948 | Many other modes, such as Mail mode, Outline mode | |
949 | and Indented Text mode, inherit all the commands | |
950 | defined in this map.") | |
951 | @end group | |
952 | @end smallexample | |
953 | ||
954 | Here is how the actual mode command is defined now: | |
955 | ||
956 | @smallexample | |
957 | @group | |
958 | (define-derived-mode text-mode nil "Text" | |
959 | "Major mode for editing text written for humans to read. | |
960 | In this mode, paragraphs are delimited only by blank or white lines. | |
961 | You can thus get the full benefit of adaptive filling | |
962 | (see the variable `adaptive-fill-mode'). | |
963 | \\@{text-mode-map@} | |
964 | Turning on Text mode runs the normal hook `text-mode-hook'." | |
965 | @end group | |
966 | @group | |
967 | (make-local-variable 'text-mode-variant) | |
968 | (setq text-mode-variant t) | |
969 | ;; @r{These two lines are a feature added recently.} | |
970 | (set (make-local-variable 'require-final-newline) | |
971 | mode-require-final-newline) | |
972 | (set (make-local-variable 'indent-line-function) 'indent-relative)) | |
973 | @end group | |
974 | @end smallexample | |
975 | ||
976 | @noindent | |
977 | (The last line is redundant nowadays, since @code{indent-relative} is | |
978 | the default value, and we'll delete it in a future version.) | |
979 | ||
980 | Here is how it was defined formerly, before | |
981 | @code{define-derived-mode} existed: | |
982 | ||
983 | @smallexample | |
984 | @group | |
985 | ;; @r{This isn't needed nowadays, since @code{define-derived-mode} does it.} | |
986 | (defvar text-mode-abbrev-table nil | |
987 | "Abbrev table used while in text mode.") | |
988 | (define-abbrev-table 'text-mode-abbrev-table ()) | |
989 | @end group | |
990 | ||
991 | @group | |
992 | (defun text-mode () | |
993 | "Major mode for editing text intended for humans to read... | |
994 | Special commands: \\@{text-mode-map@} | |
995 | @end group | |
996 | @group | |
997 | Turning on text-mode runs the hook `text-mode-hook'." | |
998 | (interactive) | |
999 | (kill-all-local-variables) | |
1000 | (use-local-map text-mode-map) | |
1001 | @end group | |
1002 | @group | |
1003 | (setq local-abbrev-table text-mode-abbrev-table) | |
1004 | (set-syntax-table text-mode-syntax-table) | |
1005 | @end group | |
1006 | @group | |
1007 | ;; @r{These four lines are absent from the current version} | |
1008 | ;; @r{not because this is done some other way, but rather} | |
1009 | ;; @r{because nowadays Text mode uses the normal definition of paragraphs.} | |
1010 | (make-local-variable 'paragraph-start) | |
1011 | (setq paragraph-start (concat "[ \t]*$\\|" page-delimiter)) | |
1012 | (make-local-variable 'paragraph-separate) | |
1013 | (setq paragraph-separate paragraph-start) | |
1014 | (make-local-variable 'indent-line-function) | |
1015 | (setq indent-line-function 'indent-relative-maybe) | |
1016 | @end group | |
1017 | @group | |
1018 | (setq mode-name "Text") | |
1019 | (setq major-mode 'text-mode) | |
1020 | (run-mode-hooks 'text-mode-hook)) ; @r{Finally, this permits the user to} | |
1021 | ; @r{customize the mode with a hook.} | |
1022 | @end group | |
1023 | @end smallexample | |
1024 | ||
1025 | @cindex @file{lisp-mode.el} | |
1026 | The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp | |
1027 | Interaction mode) have more features than Text mode and the code is | |
1028 | correspondingly more complicated. Here are excerpts from | |
1029 | @file{lisp-mode.el} that illustrate how these modes are written. | |
1030 | ||
1031 | @cindex syntax table example | |
1032 | @smallexample | |
1033 | @group | |
1034 | ;; @r{Create mode-specific table variables.} | |
1035 | (defvar lisp-mode-syntax-table nil "") | |
1036 | (defvar lisp-mode-abbrev-table nil "") | |
1037 | @end group | |
1038 | ||
1039 | @group | |
1040 | (defvar emacs-lisp-mode-syntax-table | |
1041 | (let ((table (make-syntax-table))) | |
1042 | (let ((i 0)) | |
1043 | @end group | |
1044 | ||
1045 | @group | |
1046 | ;; @r{Set syntax of chars up to @samp{0} to say they are} | |
1047 | ;; @r{part of symbol names but not words.} | |
1048 | ;; @r{(The digit @samp{0} is @code{48} in the @acronym{ASCII} character set.)} | |
1049 | (while (< i ?0) | |
1050 | (modify-syntax-entry i "_ " table) | |
1051 | (setq i (1+ i))) | |
1052 | ;; @r{@dots{} similar code follows for other character ranges.} | |
1053 | @end group | |
1054 | @group | |
1055 | ;; @r{Then set the syntax codes for characters that are special in Lisp.} | |
1056 | (modify-syntax-entry ? " " table) | |
1057 | (modify-syntax-entry ?\t " " table) | |
1058 | (modify-syntax-entry ?\f " " table) | |
1059 | (modify-syntax-entry ?\n "> " table) | |
1060 | @end group | |
1061 | @group | |
1062 | ;; @r{Give CR the same syntax as newline, for selective-display.} | |
1063 | (modify-syntax-entry ?\^m "> " table) | |
1064 | (modify-syntax-entry ?\; "< " table) | |
1065 | (modify-syntax-entry ?` "' " table) | |
1066 | (modify-syntax-entry ?' "' " table) | |
1067 | (modify-syntax-entry ?, "' " table) | |
1068 | @end group | |
1069 | @group | |
1070 | ;; @r{@dots{}likewise for many other characters@dots{}} | |
1071 | (modify-syntax-entry ?\( "() " table) | |
1072 | (modify-syntax-entry ?\) ")( " table) | |
1073 | (modify-syntax-entry ?\[ "(] " table) | |
1074 | (modify-syntax-entry ?\] ")[ " table)) | |
1075 | table)) | |
1076 | @end group | |
1077 | @group | |
1078 | ;; @r{Create an abbrev table for lisp-mode.} | |
1079 | (define-abbrev-table 'lisp-mode-abbrev-table ()) | |
1080 | @end group | |
1081 | @end smallexample | |
1082 | ||
1083 | The three modes for Lisp share much of their code. For instance, | |
1084 | each calls the following function to set various variables: | |
1085 | ||
1086 | @smallexample | |
1087 | @group | |
1088 | (defun lisp-mode-variables (lisp-syntax) | |
1089 | (when lisp-syntax | |
1090 | (set-syntax-table lisp-mode-syntax-table)) | |
1091 | (setq local-abbrev-table lisp-mode-abbrev-table) | |
1092 | @dots{} | |
1093 | @end group | |
1094 | @end smallexample | |
1095 | ||
1096 | In Lisp and most programming languages, we want the paragraph | |
1097 | commands to treat only blank lines as paragraph separators. And the | |
1098 | modes should understand the Lisp conventions for comments. The rest of | |
1099 | @code{lisp-mode-variables} sets this up: | |
1100 | ||
1101 | @smallexample | |
1102 | @group | |
1103 | (make-local-variable 'paragraph-start) | |
1104 | (setq paragraph-start (concat page-delimiter "\\|$" )) | |
1105 | (make-local-variable 'paragraph-separate) | |
1106 | (setq paragraph-separate paragraph-start) | |
1107 | @dots{} | |
1108 | @end group | |
1109 | @group | |
1110 | (make-local-variable 'comment-indent-function) | |
1111 | (setq comment-indent-function 'lisp-comment-indent)) | |
1112 | @dots{} | |
1113 | @end group | |
1114 | @end smallexample | |
1115 | ||
1116 | Each of the different Lisp modes has a slightly different keymap. For | |
1117 | example, Lisp mode binds @kbd{C-c C-z} to @code{run-lisp}, but the other | |
1118 | Lisp modes do not. However, all Lisp modes have some commands in | |
1119 | common. The following code sets up the common commands: | |
1120 | ||
1121 | @smallexample | |
1122 | @group | |
1123 | (defvar shared-lisp-mode-map () | |
1124 | "Keymap for commands shared by all sorts of Lisp modes.") | |
1125 | ||
1126 | ;; @r{Putting this @code{if} after the @code{defvar} is an older style.} | |
1127 | (if shared-lisp-mode-map | |
1128 | () | |
1129 | (setq shared-lisp-mode-map (make-sparse-keymap)) | |
1130 | (define-key shared-lisp-mode-map "\e\C-q" 'indent-sexp) | |
1131 | (define-key shared-lisp-mode-map "\177" | |
1132 | 'backward-delete-char-untabify)) | |
1133 | @end group | |
1134 | @end smallexample | |
1135 | ||
1136 | @noindent | |
1137 | And here is the code to set up the keymap for Lisp mode: | |
1138 | ||
1139 | @smallexample | |
1140 | @group | |
1141 | (defvar lisp-mode-map () | |
1142 | "Keymap for ordinary Lisp mode...") | |
1143 | ||
1144 | (if lisp-mode-map | |
1145 | () | |
1146 | (setq lisp-mode-map (make-sparse-keymap)) | |
1147 | (set-keymap-parent lisp-mode-map shared-lisp-mode-map) | |
1148 | (define-key lisp-mode-map "\e\C-x" 'lisp-eval-defun) | |
1149 | (define-key lisp-mode-map "\C-c\C-z" 'run-lisp)) | |
1150 | @end group | |
1151 | @end smallexample | |
1152 | ||
1153 | Finally, here is the complete major mode function definition for | |
1154 | Lisp mode. | |
1155 | ||
1156 | @smallexample | |
1157 | @group | |
1158 | (defun lisp-mode () | |
1159 | "Major mode for editing Lisp code for Lisps other than GNU Emacs Lisp. | |
1160 | Commands: | |
1161 | Delete converts tabs to spaces as it moves back. | |
1162 | Blank lines separate paragraphs. Semicolons start comments. | |
1163 | \\@{lisp-mode-map@} | |
1164 | Note that `run-lisp' may be used either to start an inferior Lisp job | |
1165 | or to switch back to an existing one. | |
1166 | @end group | |
1167 | ||
1168 | @group | |
1169 | Entry to this mode calls the value of `lisp-mode-hook' | |
1170 | if that value is non-nil." | |
1171 | (interactive) | |
1172 | (kill-all-local-variables) | |
1173 | @end group | |
1174 | @group | |
1175 | (use-local-map lisp-mode-map) ; @r{Select the mode's keymap.} | |
1176 | (setq major-mode 'lisp-mode) ; @r{This is how @code{describe-mode}} | |
1177 | ; @r{finds out what to describe.} | |
1178 | (setq mode-name "Lisp") ; @r{This goes into the mode line.} | |
1179 | (lisp-mode-variables t) ; @r{This defines various variables.} | |
1180 | (make-local-variable 'comment-start-skip) | |
1181 | (setq comment-start-skip | |
1182 | "\\(\\(^\\|[^\\\\\n]\\)\\(\\\\\\\\\\)*\\)\\(;+\\|#|\\) *") | |
1183 | (make-local-variable 'font-lock-keywords-case-fold-search) | |
1184 | (setq font-lock-keywords-case-fold-search t) | |
1185 | @end group | |
1186 | @group | |
1187 | (setq imenu-case-fold-search t) | |
1188 | (set-syntax-table lisp-mode-syntax-table) | |
1189 | (run-mode-hooks 'lisp-mode-hook)) ; @r{This permits the user to use a} | |
1190 | ; @r{hook to customize the mode.} | |
1191 | @end group | |
1192 | @end smallexample | |
1193 | ||
1194 | @node Minor Modes | |
1195 | @section Minor Modes | |
1196 | @cindex minor mode | |
1197 | ||
1198 | A @dfn{minor mode} provides features that users may enable or disable | |
1199 | independently of the choice of major mode. Minor modes can be enabled | |
1200 | individually or in combination. Minor modes would be better named | |
1201 | ``generally available, optional feature modes,'' except that such a name | |
1202 | would be unwieldy. | |
1203 | ||
1204 | A minor mode is not usually meant as a variation of a single major mode. | |
1205 | Usually they are general and can apply to many major modes. For | |
1206 | example, Auto Fill mode works with any major mode that permits text | |
1207 | insertion. To be general, a minor mode must be effectively independent | |
1208 | of the things major modes do. | |
1209 | ||
1210 | A minor mode is often much more difficult to implement than a major | |
1211 | mode. One reason is that you should be able to activate and deactivate | |
1212 | minor modes in any order. A minor mode should be able to have its | |
1213 | desired effect regardless of the major mode and regardless of the other | |
1214 | minor modes in effect. | |
1215 | ||
1216 | Often the biggest problem in implementing a minor mode is finding a | |
1217 | way to insert the necessary hook into the rest of Emacs. Minor mode | |
1218 | keymaps make this easier than it used to be. | |
1219 | ||
1220 | @defvar minor-mode-list | |
1221 | The value of this variable is a list of all minor mode commands. | |
1222 | @end defvar | |
1223 | ||
1224 | @menu | |
1225 | * Minor Mode Conventions:: Tips for writing a minor mode. | |
1226 | * Keymaps and Minor Modes:: How a minor mode can have its own keymap. | |
1227 | * Defining Minor Modes:: A convenient facility for defining minor modes. | |
1228 | @end menu | |
1229 | ||
1230 | @node Minor Mode Conventions | |
1231 | @subsection Conventions for Writing Minor Modes | |
1232 | @cindex minor mode conventions | |
1233 | @cindex conventions for writing minor modes | |
1234 | ||
1235 | There are conventions for writing minor modes just as there are for | |
1236 | major modes. Several of the major mode conventions apply to minor | |
1237 | modes as well: those regarding the name of the mode initialization | |
1238 | function, the names of global symbols, the use of a hook at the end of | |
1239 | the initialization function, and the use of keymaps and other tables. | |
1240 | ||
1241 | In addition, there are several conventions that are specific to | |
1242 | minor modes. (The easiest way to follow all the conventions is to use | |
1243 | the macro @code{define-minor-mode}; @ref{Defining Minor Modes}.) | |
1244 | ||
1245 | @itemize @bullet | |
1246 | @item | |
1247 | @cindex mode variable | |
1248 | Make a variable whose name ends in @samp{-mode} to control the minor | |
1249 | mode. We call this the @dfn{mode variable}. The minor mode command | |
1250 | should set this variable (@code{nil} to disable; anything else to | |
1251 | enable). | |
1252 | ||
1253 | If possible, implement the mode so that setting the variable | |
1254 | automatically enables or disables the mode. Then the minor mode command | |
1255 | does not need to do anything except set the variable. | |
1256 | ||
1257 | This variable is used in conjunction with the @code{minor-mode-alist} to | |
1258 | display the minor mode name in the mode line. It can also enable | |
1259 | or disable a minor mode keymap. Individual commands or hooks can also | |
1260 | check the variable's value. | |
1261 | ||
1262 | If you want the minor mode to be enabled separately in each buffer, | |
1263 | make the variable buffer-local. | |
1264 | ||
1265 | @item | |
1266 | Define a command whose name is the same as the mode variable. | |
1267 | Its job is to enable and disable the mode by setting the variable. | |
1268 | ||
1269 | The command should accept one optional argument. If the argument is | |
1270 | @code{nil}, it should toggle the mode (turn it on if it is off, and | |
1271 | off if it is on). It should turn the mode on if the argument is a | |
1272 | positive integer, the symbol @code{t}, or a list whose @sc{car} is one | |
1273 | of those. It should turn the mode off if the argument is a negative | |
1274 | integer or zero, the symbol @code{-}, or a list whose @sc{car} is a | |
1275 | negative integer or zero. The meaning of other arguments is not | |
1276 | specified. | |
1277 | ||
1278 | Here is an example taken from the definition of @code{transient-mark-mode}. | |
1279 | It shows the use of @code{transient-mark-mode} as a variable that enables or | |
1280 | disables the mode's behavior, and also shows the proper way to toggle, | |
1281 | enable or disable the minor mode based on the raw prefix argument value. | |
1282 | ||
1283 | @smallexample | |
1284 | @group | |
1285 | (setq transient-mark-mode | |
1286 | (if (null arg) (not transient-mark-mode) | |
1287 | (> (prefix-numeric-value arg) 0))) | |
1288 | @end group | |
1289 | @end smallexample | |
1290 | ||
1291 | @item | |
1292 | Add an element to @code{minor-mode-alist} for each minor mode | |
1293 | (@pxref{Definition of minor-mode-alist}), if you want to indicate the | |
1294 | minor mode in the mode line. This element should be a list of the | |
1295 | following form: | |
1296 | ||
1297 | @smallexample | |
1298 | (@var{mode-variable} @var{string}) | |
1299 | @end smallexample | |
1300 | ||
1301 | Here @var{mode-variable} is the variable that controls enabling of the | |
1302 | minor mode, and @var{string} is a short string, starting with a space, | |
1303 | to represent the mode in the mode line. These strings must be short so | |
1304 | that there is room for several of them at once. | |
1305 | ||
1306 | When you add an element to @code{minor-mode-alist}, use @code{assq} to | |
1307 | check for an existing element, to avoid duplication. For example: | |
1308 | ||
1309 | @smallexample | |
1310 | @group | |
1311 | (unless (assq 'leif-mode minor-mode-alist) | |
1312 | (setq minor-mode-alist | |
1313 | (cons '(leif-mode " Leif") minor-mode-alist))) | |
1314 | @end group | |
1315 | @end smallexample | |
1316 | ||
1317 | @noindent | |
1318 | or like this, using @code{add-to-list} (@pxref{List Variables}): | |
1319 | ||
1320 | @smallexample | |
1321 | @group | |
1322 | (add-to-list 'minor-mode-alist '(leif-mode " Leif")) | |
1323 | @end group | |
1324 | @end smallexample | |
1325 | @end itemize | |
1326 | ||
1327 | Global minor modes distributed with Emacs should if possible support | |
1328 | enabling and disabling via Custom (@pxref{Customization}). To do this, | |
1329 | the first step is to define the mode variable with @code{defcustom}, and | |
1330 | specify @code{:type boolean}. | |
1331 | ||
1332 | If just setting the variable is not sufficient to enable the mode, you | |
1333 | should also specify a @code{:set} method which enables the mode by | |
1334 | invoking the mode command. Note in the variable's documentation string that | |
1335 | setting the variable other than via Custom may not take effect. | |
1336 | ||
1337 | Also mark the definition with an autoload cookie (@pxref{autoload cookie}), | |
1338 | and specify a @code{:require} so that customizing the variable will load | |
1339 | the library that defines the mode. This will copy suitable definitions | |
1340 | into @file{loaddefs.el} so that users can use @code{customize-option} to | |
1341 | enable the mode. For example: | |
1342 | ||
1343 | @smallexample | |
1344 | @group | |
1345 | ||
1346 | ;;;###autoload | |
1347 | (defcustom msb-mode nil | |
1348 | "Toggle msb-mode. | |
1349 | Setting this variable directly does not take effect; | |
1350 | use either \\[customize] or the function `msb-mode'." | |
1351 | :set 'custom-set-minor-mode | |
1352 | :initialize 'custom-initialize-default | |
1353 | :version "20.4" | |
1354 | :type 'boolean | |
1355 | :group 'msb | |
1356 | :require 'msb) | |
1357 | @end group | |
1358 | @end smallexample | |
1359 | ||
1360 | @node Keymaps and Minor Modes | |
1361 | @subsection Keymaps and Minor Modes | |
1362 | ||
1363 | Each minor mode can have its own keymap, which is active when the mode | |
1364 | is enabled. To set up a keymap for a minor mode, add an element to the | |
1365 | alist @code{minor-mode-map-alist}. @xref{Definition of minor-mode-map-alist}. | |
1366 | ||
1367 | @cindex @code{self-insert-command}, minor modes | |
1368 | One use of minor mode keymaps is to modify the behavior of certain | |
1369 | self-inserting characters so that they do something else as well as | |
1370 | self-insert. In general, this is the only way to do that, since the | |
1371 | facilities for customizing @code{self-insert-command} are limited to | |
1372 | special cases (designed for abbrevs and Auto Fill mode). (Do not try | |
1373 | substituting your own definition of @code{self-insert-command} for the | |
1374 | standard one. The editor command loop handles this function specially.) | |
1375 | ||
1376 | The key sequences bound in a minor mode should consist of @kbd{C-c} | |
1377 | followed by one of @kbd{.,/?`'"[]\|~!#$%^&*()-_+=}. (The other | |
1378 | punctuation characters are reserved for major modes.) | |
1379 | ||
1380 | @node Defining Minor Modes | |
1381 | @subsection Defining Minor Modes | |
1382 | ||
1383 | The macro @code{define-minor-mode} offers a convenient way of | |
1384 | implementing a mode in one self-contained definition. | |
1385 | ||
1386 | @defmac define-minor-mode mode doc [init-value [lighter [keymap]]] keyword-args@dots{} body@dots{} | |
1387 | This macro defines a new minor mode whose name is @var{mode} (a | |
1388 | symbol). It defines a command named @var{mode} to toggle the minor | |
1389 | mode, with @var{doc} as its documentation string. It also defines a | |
1390 | variable named @var{mode}, which is set to @code{t} or @code{nil} by | |
1391 | enabling or disabling the mode. The variable is initialized to | |
1392 | @var{init-value}. Except in unusual circumstances (see below), this | |
1393 | value must be @code{nil}. | |
1394 | ||
1395 | The string @var{lighter} says what to display in the mode line | |
1396 | when the mode is enabled; if it is @code{nil}, the mode is not displayed | |
1397 | in the mode line. | |
1398 | ||
1399 | The optional argument @var{keymap} specifies the keymap for the minor mode. | |
1400 | It can be a variable name, whose value is the keymap, or it can be an alist | |
1401 | specifying bindings in this form: | |
1402 | ||
1403 | @example | |
1404 | (@var{key-sequence} . @var{definition}) | |
1405 | @end example | |
1406 | ||
1407 | The above three arguments @var{init-value}, @var{lighter}, and | |
1408 | @var{keymap} can be (partially) omitted when @var{keyword-args} are | |
1409 | used. The @var{keyword-args} consist of keywords followed by | |
1410 | corresponding values. A few keywords have special meanings: | |
1411 | ||
1412 | @table @code | |
1413 | @item :group @var{group} | |
1414 | Custom group name to use in all generated @code{defcustom} forms. | |
1415 | Defaults to @var{mode} without the possible trailing @samp{-mode}. | |
1416 | @strong{Warning:} don't use this default group name unless you have | |
1417 | written a @code{defgroup} to define that group properly. @xref{Group | |
1418 | Definitions}. | |
1419 | ||
1420 | @item :global @var{global} | |
1421 | If non-@code{nil}, this specifies that the minor mode should be global | |
1422 | rather than buffer-local. It defaults to @code{nil}. | |
1423 | ||
1424 | One of the effects of making a minor mode global is that the | |
1425 | @var{mode} variable becomes a customization variable. Toggling it | |
1426 | through the Custom interface turns the mode on and off, and its value | |
1427 | can be saved for future Emacs sessions (@pxref{Saving | |
1428 | Customizations,,, emacs, The GNU Emacs Manual}. For the saved | |
1429 | variable to work, you should ensure that the @code{define-minor-mode} | |
1430 | form is evaluated each time Emacs starts; for packages that are not | |
1431 | part of Emacs, the easiest way to do this is to specify a | |
1432 | @code{:require} keyword. | |
1433 | ||
1434 | @item :init-value @var{init-value} | |
1435 | This is equivalent to specifying @var{init-value} positionally. | |
1436 | ||
1437 | @item :lighter @var{lighter} | |
1438 | This is equivalent to specifying @var{lighter} positionally. | |
1439 | ||
1440 | @item :keymap @var{keymap} | |
1441 | This is equivalent to specifying @var{keymap} positionally. | |
1442 | @end table | |
1443 | ||
1444 | Any other keyword arguments are passed directly to the | |
1445 | @code{defcustom} generated for the variable @var{mode}. | |
1446 | ||
1447 | The command named @var{mode} first performs the standard actions such | |
1448 | as setting the variable named @var{mode} and then executes the | |
1449 | @var{body} forms, if any. It finishes by running the mode hook | |
1450 | variable @code{@var{mode}-hook}. | |
1451 | @end defmac | |
1452 | ||
1453 | The initial value must be @code{nil} except in cases where (1) the | |
1454 | mode is preloaded in Emacs, or (2) it is painless for loading to | |
1455 | enable the mode even though the user did not request it. For | |
1456 | instance, if the mode has no effect unless something else is enabled, | |
1457 | and will always be loaded by that time, enabling it by default is | |
1458 | harmless. But these are unusual circumstances. Normally, the | |
1459 | initial value must be @code{nil}. | |
1460 | ||
1461 | @findex easy-mmode-define-minor-mode | |
1462 | The name @code{easy-mmode-define-minor-mode} is an alias | |
1463 | for this macro. | |
1464 | ||
1465 | Here is an example of using @code{define-minor-mode}: | |
1466 | ||
1467 | @smallexample | |
1468 | (define-minor-mode hungry-mode | |
1469 | "Toggle Hungry mode. | |
1470 | With no argument, this command toggles the mode. | |
1471 | Non-null prefix argument turns on the mode. | |
1472 | Null prefix argument turns off the mode. | |
1473 | ||
1474 | When Hungry mode is enabled, the control delete key | |
1475 | gobbles all preceding whitespace except the last. | |
1476 | See the command \\[hungry-electric-delete]." | |
1477 | ;; The initial value. | |
1478 | nil | |
1479 | ;; The indicator for the mode line. | |
1480 | " Hungry" | |
1481 | ;; The minor mode bindings. | |
1482 | '(("\C-\^?" . hungry-electric-delete)) | |
1483 | :group 'hunger) | |
1484 | @end smallexample | |
1485 | ||
1486 | @noindent | |
1487 | This defines a minor mode named ``Hungry mode,'' a command named | |
1488 | @code{hungry-mode} to toggle it, a variable named @code{hungry-mode} | |
1489 | which indicates whether the mode is enabled, and a variable named | |
1490 | @code{hungry-mode-map} which holds the keymap that is active when the | |
1491 | mode is enabled. It initializes the keymap with a key binding for | |
1492 | @kbd{C-@key{DEL}}. It puts the variable @code{hungry-mode} into | |
1493 | custom group @code{hunger}. There are no @var{body} forms---many | |
1494 | minor modes don't need any. | |
1495 | ||
1496 | Here's an equivalent way to write it: | |
1497 | ||
1498 | @smallexample | |
1499 | (define-minor-mode hungry-mode | |
1500 | "Toggle Hungry mode. | |
1501 | With no argument, this command toggles the mode. | |
1502 | Non-null prefix argument turns on the mode. | |
1503 | Null prefix argument turns off the mode. | |
1504 | ||
1505 | When Hungry mode is enabled, the control delete key | |
1506 | gobbles all preceding whitespace except the last. | |
1507 | See the command \\[hungry-electric-delete]." | |
1508 | ;; The initial value. | |
1509 | :init-value nil | |
1510 | ;; The indicator for the mode line. | |
1511 | :lighter " Hungry" | |
1512 | ;; The minor mode bindings. | |
1513 | :keymap | |
1514 | '(("\C-\^?" . hungry-electric-delete) | |
1515 | ("\C-\M-\^?" | |
1516 | . (lambda () | |
1517 | (interactive) | |
1518 | (hungry-electric-delete t)))) | |
1519 | :group 'hunger) | |
1520 | @end smallexample | |
1521 | ||
1522 | @defmac define-globalized-minor-mode global-mode mode turn-on keyword-args@dots{} | |
1523 | This defines a global toggle named @var{global-mode} whose meaning is | |
1524 | to enable or disable the buffer-local minor mode @var{mode} in all | |
1525 | buffers. To turn on the minor mode in a buffer, it uses the function | |
1526 | @var{turn-on}; to turn off the minor mode, it calls @code{mode} with | |
1527 | @minus{}1 as argument. | |
1528 | ||
1529 | Globally enabling the mode also affects buffers subsequently created | |
1530 | by visiting files, and buffers that use a major mode other than | |
1531 | Fundamental mode; but it does not detect the creation of a new buffer | |
1532 | in Fundamental mode. | |
1533 | ||
1534 | This defines the customization option @var{global-mode} (@pxref{Customization}), | |
1535 | which can be toggled in the Custom interface to turn the minor mode on | |
1536 | and off. As with @code{define-minor-mode}, you should ensure that the | |
1537 | @code{define-globalized-minor-mode} form is evaluated each time Emacs | |
1538 | starts, for example by providing a @code{:require} keyword. | |
1539 | ||
1540 | Use @code{:group @var{group}} in @var{keyword-args} to specify the | |
1541 | custom group for the mode variable of the global minor mode. | |
1542 | @end defmac | |
1543 | ||
1544 | @node Mode Line Format | |
1545 | @section Mode-Line Format | |
1546 | @cindex mode line | |
1547 | ||
1548 | Each Emacs window (aside from minibuffer windows) typically has a mode | |
1549 | line at the bottom, which displays status information about the buffer | |
1550 | displayed in the window. The mode line contains information about the | |
1551 | buffer, such as its name, associated file, depth of recursive editing, | |
1552 | and major and minor modes. A window can also have a @dfn{header | |
1553 | line}, which is much like the mode line but appears at the top of the | |
1554 | window. | |
1555 | ||
1556 | This section describes how to control the contents of the mode line | |
1557 | and header line. We include it in this chapter because much of the | |
1558 | information displayed in the mode line relates to the enabled major and | |
1559 | minor modes. | |
1560 | ||
1561 | @menu | |
1562 | * Base: Mode Line Basics. Basic ideas of mode line control. | |
1563 | * Data: Mode Line Data. The data structure that controls the mode line. | |
1564 | * Top: Mode Line Top. The top level variable, mode-line-format. | |
1565 | * Mode Line Variables:: Variables used in that data structure. | |
1566 | * %-Constructs:: Putting information into a mode line. | |
1567 | * Properties in Mode:: Using text properties in the mode line. | |
1568 | * Header Lines:: Like a mode line, but at the top. | |
1569 | * Emulating Mode Line:: Formatting text as the mode line would. | |
1570 | @end menu | |
1571 | ||
1572 | @node Mode Line Basics | |
1573 | @subsection Mode Line Basics | |
1574 | ||
1575 | @code{mode-line-format} is a buffer-local variable that holds a | |
1576 | @dfn{mode line construct}, a kind of template, which controls what is | |
1577 | displayed on the mode line of the current buffer. The value of | |
1578 | @code{header-line-format} specifies the buffer's header line in the | |
1579 | same way. All windows for the same buffer use the same | |
1580 | @code{mode-line-format} and @code{header-line-format}. | |
1581 | ||
1582 | For efficiency, Emacs does not continuously recompute the mode | |
1583 | line and header line of a window. It does so when circumstances | |
1584 | appear to call for it---for instance, if you change the window | |
1585 | configuration, switch buffers, narrow or widen the buffer, scroll, or | |
1586 | change the buffer's modification status. If you modify any of the | |
1587 | variables referenced by @code{mode-line-format} (@pxref{Mode Line | |
1588 | Variables}), or any other variables and data structures that affect | |
1589 | how text is displayed (@pxref{Display}), you may want to force an | |
1590 | update of the mode line so as to display the new information or | |
1591 | display it in the new way. | |
1592 | ||
1593 | @defun force-mode-line-update &optional all | |
1594 | Force redisplay of the current buffer's mode line and header line. | |
1595 | The next redisplay will update the mode line and header line based on | |
1596 | the latest values of all relevant variables. With optional | |
1597 | non-@code{nil} @var{all}, force redisplay of all mode lines and header | |
1598 | lines. | |
1599 | ||
1600 | This function also forces recomputation of the menu bar menus | |
1601 | and the frame title. | |
1602 | @end defun | |
1603 | ||
1604 | The selected window's mode line is usually displayed in a different | |
1605 | color using the face @code{mode-line}. Other windows' mode lines | |
1606 | appear in the face @code{mode-line-inactive} instead. @xref{Faces}. | |
1607 | ||
1608 | @node Mode Line Data | |
1609 | @subsection The Data Structure of the Mode Line | |
1610 | @cindex mode-line construct | |
1611 | ||
1612 | The mode-line contents are controlled by a data structure called a | |
1613 | @dfn{mode-line construct}, made up of lists, strings, symbols, and | |
1614 | numbers kept in buffer-local variables. Each data type has a specific | |
1615 | meaning for the mode-line appearance, as described below. The same | |
1616 | data structure is used for constructing frame titles (@pxref{Frame | |
1617 | Titles}) and header lines (@pxref{Header Lines}). | |
1618 | ||
1619 | A mode-line construct may be as simple as a fixed string of text, | |
1620 | but it usually specifies how to combine fixed strings with variables' | |
1621 | values to construct the text. Many of these variables are themselves | |
1622 | defined to have mode-line constructs as their values. | |
1623 | ||
1624 | Here are the meanings of various data types as mode-line constructs: | |
1625 | ||
1626 | @table @code | |
1627 | @cindex percent symbol in mode line | |
1628 | @item @var{string} | |
1629 | A string as a mode-line construct appears verbatim except for | |
1630 | @dfn{@code{%}-constructs} in it. These stand for substitution of | |
1631 | other data; see @ref{%-Constructs}. | |
1632 | ||
1633 | If parts of the string have @code{face} properties, they control | |
1634 | display of the text just as they would text in the buffer. Any | |
1635 | characters which have no @code{face} properties are displayed, by | |
1636 | default, in the face @code{mode-line} or @code{mode-line-inactive} | |
1637 | (@pxref{Standard Faces,,, emacs, The GNU Emacs Manual}). The | |
1638 | @code{help-echo} and @code{local-map} properties in @var{string} have | |
1639 | special meanings. @xref{Properties in Mode}. | |
1640 | ||
1641 | @item @var{symbol} | |
1642 | A symbol as a mode-line construct stands for its value. The value of | |
1643 | @var{symbol} is used as a mode-line construct, in place of @var{symbol}. | |
1644 | However, the symbols @code{t} and @code{nil} are ignored, as is any | |
1645 | symbol whose value is void. | |
1646 | ||
1647 | There is one exception: if the value of @var{symbol} is a string, it is | |
1648 | displayed verbatim: the @code{%}-constructs are not recognized. | |
1649 | ||
1650 | Unless @var{symbol} is marked as ``risky'' (i.e., it has a | |
1651 | non-@code{nil} @code{risky-local-variable} property), all text | |
1652 | properties specified in @var{symbol}'s value are ignored. This | |
1653 | includes the text properties of strings in @var{symbol}'s value, as | |
1654 | well as all @code{:eval} and @code{:propertize} forms in it. (The | |
1655 | reason for this is security: non-risky variables could be set | |
1656 | automatically from file variables without prompting the user.) | |
1657 | ||
1658 | @item (@var{string} @var{rest}@dots{}) | |
1659 | @itemx (@var{list} @var{rest}@dots{}) | |
1660 | A list whose first element is a string or list means to process all the | |
1661 | elements recursively and concatenate the results. This is the most | |
1662 | common form of mode-line construct. | |
1663 | ||
1664 | @item (:eval @var{form}) | |
1665 | A list whose first element is the symbol @code{:eval} says to evaluate | |
1666 | @var{form}, and use the result as a string to display. Make sure this | |
1667 | evaluation cannot load any files, as doing so could cause infinite | |
1668 | recursion. | |
1669 | ||
1670 | @item (:propertize @var{elt} @var{props}@dots{}) | |
1671 | A list whose first element is the symbol @code{:propertize} says to | |
1672 | process the mode-line construct @var{elt} recursively, then add the text | |
1673 | properties specified by @var{props} to the result. The argument | |
1674 | @var{props} should consist of zero or more pairs @var{text-property} | |
1675 | @var{value}. (This feature is new as of Emacs 22.1.) | |
1676 | ||
1677 | @item (@var{symbol} @var{then} @var{else}) | |
1678 | A list whose first element is a symbol that is not a keyword specifies | |
1679 | a conditional. Its meaning depends on the value of @var{symbol}. If | |
1680 | @var{symbol} has a non-@code{nil} value, the second element, | |
1681 | @var{then}, is processed recursively as a mode-line element. | |
1682 | Otherwise, the third element, @var{else}, is processed recursively. | |
1683 | You may omit @var{else}; then the mode-line element displays nothing | |
1684 | if the value of @var{symbol} is @code{nil} or void. | |
1685 | ||
1686 | @item (@var{width} @var{rest}@dots{}) | |
1687 | A list whose first element is an integer specifies truncation or | |
1688 | padding of the results of @var{rest}. The remaining elements | |
1689 | @var{rest} are processed recursively as mode-line constructs and | |
1690 | concatenated together. When @var{width} is positive, the result is | |
1691 | space filled on the right if its width is less than @var{width}. When | |
1692 | @var{width} is negative, the result is truncated on the right to | |
1693 | @minus{}@var{width} columns if its width exceeds @minus{}@var{width}. | |
1694 | ||
1695 | For example, the usual way to show what percentage of a buffer is above | |
1696 | the top of the window is to use a list like this: @code{(-3 "%p")}. | |
1697 | @end table | |
1698 | ||
1699 | @node Mode Line Top | |
1700 | @subsection The Top Level of Mode Line Control | |
1701 | ||
1702 | The variable in overall control of the mode line is | |
1703 | @code{mode-line-format}. | |
1704 | ||
1705 | @defvar mode-line-format | |
1706 | The value of this variable is a mode-line construct that controls the | |
1707 | contents of the mode-line. It is always buffer-local in all buffers. | |
1708 | ||
1709 | If you set this variable to @code{nil} in a buffer, that buffer does | |
1710 | not have a mode line. (A window that is just one line tall never | |
1711 | displays a mode line.) | |
1712 | @end defvar | |
1713 | ||
1714 | The default value of @code{mode-line-format} is designed to use the | |
1715 | values of other variables such as @code{mode-line-position} and | |
1716 | @code{mode-line-modes} (which in turn incorporates the values of the | |
1717 | variables @code{mode-name} and @code{minor-mode-alist}). Very few | |
1718 | modes need to alter @code{mode-line-format} itself. For most | |
1719 | purposes, it is sufficient to alter some of the variables that | |
1720 | @code{mode-line-format} either directly or indirectly refers to. | |
1721 | ||
1722 | If you do alter @code{mode-line-format} itself, the new value should | |
1723 | use the same variables that appear in the default value (@pxref{Mode | |
1724 | Line Variables}), rather than duplicating their contents or displaying | |
1725 | the information in another fashion. This way, customizations made by | |
1726 | the user or by Lisp programs (such as @code{display-time} and major | |
1727 | modes) via changes to those variables remain effective. | |
1728 | ||
1729 | Here is an example of a @code{mode-line-format} that might be | |
1730 | useful for @code{shell-mode}, since it contains the host name and default | |
1731 | directory. | |
1732 | ||
1733 | @example | |
1734 | @group | |
1735 | (setq mode-line-format | |
1736 | (list "-" | |
1737 | 'mode-line-mule-info | |
1738 | 'mode-line-modified | |
1739 | 'mode-line-frame-identification | |
1740 | "%b--" | |
1741 | @end group | |
1742 | @group | |
1743 | ;; @r{Note that this is evaluated while making the list.} | |
1744 | ;; @r{It makes a mode-line construct which is just a string.} | |
1745 | (getenv "HOST") | |
1746 | @end group | |
1747 | ":" | |
1748 | 'default-directory | |
1749 | " " | |
1750 | 'global-mode-string | |
1751 | " %[(" | |
1752 | '(:eval (mode-line-mode-name)) | |
1753 | 'mode-line-process | |
1754 | 'minor-mode-alist | |
1755 | "%n" | |
1756 | ")%]--" | |
1757 | @group | |
1758 | '(which-func-mode ("" which-func-format "--")) | |
1759 | '(line-number-mode "L%l--") | |
1760 | '(column-number-mode "C%c--") | |
1761 | '(-3 "%p") | |
1762 | "-%-")) | |
1763 | @end group | |
1764 | @end example | |
1765 | ||
1766 | @noindent | |
1767 | (The variables @code{line-number-mode}, @code{column-number-mode} | |
1768 | and @code{which-func-mode} enable particular minor modes; as usual, | |
1769 | these variable names are also the minor mode command names.) | |
1770 | ||
1771 | @node Mode Line Variables | |
1772 | @subsection Variables Used in the Mode Line | |
1773 | ||
1774 | This section describes variables incorporated by the standard value | |
1775 | of @code{mode-line-format} into the text of the mode line. There is | |
1776 | nothing inherently special about these variables; any other variables | |
1777 | could have the same effects on the mode line if | |
1778 | @code{mode-line-format}'s value were changed to use them. However, | |
1779 | various parts of Emacs set these variables on the understanding that | |
1780 | they will control parts of the mode line; therefore, practically | |
1781 | speaking, it is essential for the mode line to use them. | |
1782 | ||
1783 | @defvar mode-line-mule-info | |
1784 | This variable holds the value of the mode-line construct that displays | |
1785 | information about the language environment, buffer coding system, and | |
1786 | current input method. @xref{Non-ASCII Characters}. | |
1787 | @end defvar | |
1788 | ||
1789 | @defvar mode-line-modified | |
1790 | This variable holds the value of the mode-line construct that displays | |
1791 | whether the current buffer is modified. | |
1792 | ||
1793 | The default value of @code{mode-line-modified} is @code{("%1*%1+")}. | |
1794 | This means that the mode line displays @samp{**} if the buffer is | |
1795 | modified, @samp{--} if the buffer is not modified, @samp{%%} if the | |
1796 | buffer is read only, and @samp{%*} if the buffer is read only and | |
1797 | modified. | |
1798 | ||
1799 | Changing this variable does not force an update of the mode line. | |
1800 | @end defvar | |
1801 | ||
1802 | @defvar mode-line-frame-identification | |
1803 | This variable identifies the current frame. The default value is | |
1804 | @code{" "} if you are using a window system which can show multiple | |
1805 | frames, or @code{"-%F "} on an ordinary terminal which shows only one | |
1806 | frame at a time. | |
1807 | @end defvar | |
1808 | ||
1809 | @defvar mode-line-buffer-identification | |
1810 | This variable identifies the buffer being displayed in the window. Its | |
1811 | default value is @code{("%12b")}, which displays the buffer name, padded | |
1812 | with spaces to at least 12 columns. | |
1813 | @end defvar | |
1814 | ||
1815 | @defvar mode-line-position | |
1816 | This variable indicates the position in the buffer. Here is a | |
1817 | simplified version of its default value. The actual default value | |
1818 | also specifies addition of the @code{help-echo} text property. | |
1819 | ||
1820 | @example | |
1821 | @group | |
1822 | ((-3 "%p") | |
1823 | (size-indication-mode (8 " of %I")) | |
1824 | @end group | |
1825 | @group | |
1826 | (line-number-mode | |
1827 | ((column-number-mode | |
1828 | (10 " (%l,%c)") | |
1829 | (6 " L%l"))) | |
1830 | ((column-number-mode | |
1831 | (5 " C%c"))))) | |
1832 | @end group | |
1833 | @end example | |
1834 | ||
1835 | This means that @code{mode-line-position} displays at least the buffer | |
1836 | percentage and possibly the buffer size, the line number and the column | |
1837 | number. | |
1838 | @end defvar | |
1839 | ||
1840 | @defvar vc-mode | |
1841 | The variable @code{vc-mode}, buffer-local in each buffer, records | |
1842 | whether the buffer's visited file is maintained with version control, | |
1843 | and, if so, which kind. Its value is a string that appears in the mode | |
1844 | line, or @code{nil} for no version control. | |
1845 | @end defvar | |
1846 | ||
1847 | @defvar mode-line-modes | |
1848 | This variable displays the buffer's major and minor modes. Here is a | |
1849 | simplified version of its default value. The real default value also | |
1850 | specifies addition of text properties. | |
1851 | ||
1852 | @example | |
1853 | @group | |
1854 | ("%[(" mode-name | |
1855 | mode-line-process minor-mode-alist | |
1856 | "%n" ")%]--") | |
1857 | @end group | |
1858 | @end example | |
1859 | ||
1860 | So @code{mode-line-modes} normally also displays the recursive editing | |
1861 | level, information on the process status and whether narrowing is in | |
1862 | effect. | |
1863 | @end defvar | |
1864 | ||
1865 | The following three variables are used in @code{mode-line-modes}: | |
1866 | ||
1867 | @defvar mode-name | |
1868 | This buffer-local variable holds the ``pretty'' name of the current | |
9cf52b11 EZ |
1869 | buffer's major mode. Each major mode should set this variable so that |
1870 | the mode name will appear in the mode line. The value does not have | |
1871 | to be a string, but can use any of the data types valid in a mode-line | |
1872 | construct (@pxref{Mode Line Data}). To compute the string that will | |
1873 | identify the mode name in the mode line, use @code{format-mode-line} | |
1874 | (@pxref{Emulating Mode Line}). | |
b8d4c8d0 GM |
1875 | @end defvar |
1876 | ||
1877 | @defvar mode-line-process | |
1878 | This buffer-local variable contains the mode-line information on process | |
1879 | status in modes used for communicating with subprocesses. It is | |
1880 | displayed immediately following the major mode name, with no intervening | |
1881 | space. For example, its value in the @samp{*shell*} buffer is | |
1882 | @code{(":%s")}, which allows the shell to display its status along | |
1883 | with the major mode as: @samp{(Shell:run)}. Normally this variable | |
1884 | is @code{nil}. | |
1885 | @end defvar | |
1886 | ||
1887 | @defvar minor-mode-alist | |
1888 | @anchor{Definition of minor-mode-alist} | |
1889 | This variable holds an association list whose elements specify how the | |
1890 | mode line should indicate that a minor mode is active. Each element of | |
1891 | the @code{minor-mode-alist} should be a two-element list: | |
1892 | ||
1893 | @example | |
1894 | (@var{minor-mode-variable} @var{mode-line-string}) | |
1895 | @end example | |
1896 | ||
1897 | More generally, @var{mode-line-string} can be any mode-line spec. It | |
1898 | appears in the mode line when the value of @var{minor-mode-variable} | |
1899 | is non-@code{nil}, and not otherwise. These strings should begin with | |
1900 | spaces so that they don't run together. Conventionally, the | |
1901 | @var{minor-mode-variable} for a specific mode is set to a | |
1902 | non-@code{nil} value when that minor mode is activated. | |
1903 | ||
1904 | @code{minor-mode-alist} itself is not buffer-local. Each variable | |
1905 | mentioned in the alist should be buffer-local if its minor mode can be | |
1906 | enabled separately in each buffer. | |
1907 | @end defvar | |
1908 | ||
1909 | @defvar global-mode-string | |
1910 | This variable holds a mode-line spec that, by default, appears in the | |
1911 | mode line just after the @code{which-func-mode} minor mode if set, | |
1912 | else after @code{mode-line-modes}. The command @code{display-time} | |
1913 | sets @code{global-mode-string} to refer to the variable | |
1914 | @code{display-time-string}, which holds a string containing the time | |
1915 | and load information. | |
1916 | ||
1917 | The @samp{%M} construct substitutes the value of | |
1918 | @code{global-mode-string}, but that is obsolete, since the variable is | |
1919 | included in the mode line from @code{mode-line-format}. | |
1920 | @end defvar | |
1921 | ||
1922 | The variable @code{default-mode-line-format} is where | |
1923 | @code{mode-line-format} usually gets its value: | |
1924 | ||
1925 | @defvar default-mode-line-format | |
1926 | This variable holds the default @code{mode-line-format} for buffers | |
1927 | that do not override it. This is the same as @code{(default-value | |
1928 | 'mode-line-format)}. | |
1929 | ||
1930 | Here is a simplified version of the default value of | |
1931 | @code{default-mode-line-format}. The real default value also | |
1932 | specifies addition of text properties. | |
1933 | ||
1934 | @example | |
1935 | @group | |
1936 | ("-" | |
1937 | mode-line-mule-info | |
1938 | mode-line-modified | |
1939 | mode-line-frame-identification | |
1940 | mode-line-buffer-identification | |
1941 | @end group | |
1942 | " " | |
1943 | mode-line-position | |
1944 | (vc-mode vc-mode) | |
1945 | " " | |
1946 | @group | |
1947 | mode-line-modes | |
1948 | (which-func-mode ("" which-func-format "--")) | |
1949 | (global-mode-string ("--" global-mode-string)) | |
1950 | "-%-") | |
1951 | @end group | |
1952 | @end example | |
1953 | @end defvar | |
1954 | ||
1955 | @node %-Constructs | |
1956 | @subsection @code{%}-Constructs in the Mode Line | |
1957 | ||
1958 | Strings used as mode-line constructs can use certain | |
1959 | @code{%}-constructs to substitute various kinds of data. Here is a | |
1960 | list of the defined @code{%}-constructs, and what they mean. In any | |
1961 | construct except @samp{%%}, you can add a decimal integer after the | |
1962 | @samp{%} to specify a minimum field width. If the width is less, the | |
1963 | field is padded with spaces to the right. | |
1964 | ||
1965 | @table @code | |
1966 | @item %b | |
1967 | The current buffer name, obtained with the @code{buffer-name} function. | |
1968 | @xref{Buffer Names}. | |
1969 | ||
1970 | @item %c | |
1971 | The current column number of point. | |
1972 | ||
1973 | @item %e | |
1974 | When Emacs is nearly out of memory for Lisp objects, a brief message | |
1975 | saying so. Otherwise, this is empty. | |
1976 | ||
1977 | @item %f | |
1978 | The visited file name, obtained with the @code{buffer-file-name} | |
1979 | function. @xref{Buffer File Name}. | |
1980 | ||
1981 | @item %F | |
1982 | The title (only on a window system) or the name of the selected frame. | |
1983 | @xref{Basic Parameters}. | |
1984 | ||
1985 | @item %i | |
1986 | The size of the accessible part of the current buffer; basically | |
1987 | @code{(- (point-max) (point-min))}. | |
1988 | ||
1989 | @item %I | |
1990 | Like @samp{%i}, but the size is printed in a more readable way by using | |
1991 | @samp{k} for 10^3, @samp{M} for 10^6, @samp{G} for 10^9, etc., to | |
1992 | abbreviate. | |
1993 | ||
1994 | @item %l | |
1995 | The current line number of point, counting within the accessible portion | |
1996 | of the buffer. | |
1997 | ||
1998 | @item %n | |
1999 | @samp{Narrow} when narrowing is in effect; nothing otherwise (see | |
2000 | @code{narrow-to-region} in @ref{Narrowing}). | |
2001 | ||
2002 | @item %p | |
2003 | The percentage of the buffer text above the @strong{top} of window, or | |
2004 | @samp{Top}, @samp{Bottom} or @samp{All}. Note that the default | |
2005 | mode-line specification truncates this to three characters. | |
2006 | ||
2007 | @item %P | |
2008 | The percentage of the buffer text that is above the @strong{bottom} of | |
2009 | the window (which includes the text visible in the window, as well as | |
2010 | the text above the top), plus @samp{Top} if the top of the buffer is | |
2011 | visible on screen; or @samp{Bottom} or @samp{All}. | |
2012 | ||
2013 | @item %s | |
2014 | The status of the subprocess belonging to the current buffer, obtained with | |
2015 | @code{process-status}. @xref{Process Information}. | |
2016 | ||
2017 | @item %t | |
2018 | Whether the visited file is a text file or a binary file. This is a | |
2019 | meaningful distinction only on certain operating systems (@pxref{MS-DOS | |
2020 | File Types}). | |
2021 | ||
2022 | @item %z | |
2023 | The mnemonics of keyboard, terminal, and buffer coding systems. | |
2024 | ||
2025 | @item %Z | |
2026 | Like @samp{%z}, but including the end-of-line format. | |
2027 | ||
2028 | @item %* | |
2029 | @samp{%} if the buffer is read only (see @code{buffer-read-only}); @* | |
2030 | @samp{*} if the buffer is modified (see @code{buffer-modified-p}); @* | |
2031 | @samp{-} otherwise. @xref{Buffer Modification}. | |
2032 | ||
2033 | @item %+ | |
2034 | @samp{*} if the buffer is modified (see @code{buffer-modified-p}); @* | |
2035 | @samp{%} if the buffer is read only (see @code{buffer-read-only}); @* | |
2036 | @samp{-} otherwise. This differs from @samp{%*} only for a modified | |
2037 | read-only buffer. @xref{Buffer Modification}. | |
2038 | ||
2039 | @item %& | |
2040 | @samp{*} if the buffer is modified, and @samp{-} otherwise. | |
2041 | ||
2042 | @item %[ | |
2043 | An indication of the depth of recursive editing levels (not counting | |
2044 | minibuffer levels): one @samp{[} for each editing level. | |
2045 | @xref{Recursive Editing}. | |
2046 | ||
2047 | @item %] | |
2048 | One @samp{]} for each recursive editing level (not counting minibuffer | |
2049 | levels). | |
2050 | ||
2051 | @item %- | |
2052 | Dashes sufficient to fill the remainder of the mode line. | |
2053 | ||
2054 | @item %% | |
2055 | The character @samp{%}---this is how to include a literal @samp{%} in a | |
2056 | string in which @code{%}-constructs are allowed. | |
2057 | @end table | |
2058 | ||
2059 | The following two @code{%}-constructs are still supported, but they are | |
2060 | obsolete, since you can get the same results with the variables | |
2061 | @code{mode-name} and @code{global-mode-string}. | |
2062 | ||
2063 | @table @code | |
2064 | @item %m | |
2065 | The value of @code{mode-name}. | |
2066 | ||
2067 | @item %M | |
2068 | The value of @code{global-mode-string}. | |
2069 | @end table | |
2070 | ||
2071 | @node Properties in Mode | |
2072 | @subsection Properties in the Mode Line | |
2073 | @cindex text properties in the mode line | |
2074 | ||
2075 | Certain text properties are meaningful in the | |
2076 | mode line. The @code{face} property affects the appearance of text; the | |
2077 | @code{help-echo} property associates help strings with the text, and | |
2078 | @code{local-map} can make the text mouse-sensitive. | |
2079 | ||
2080 | There are four ways to specify text properties for text in the mode | |
2081 | line: | |
2082 | ||
2083 | @enumerate | |
2084 | @item | |
2085 | Put a string with a text property directly into the mode-line data | |
2086 | structure. | |
2087 | ||
2088 | @item | |
2089 | Put a text property on a mode-line %-construct such as @samp{%12b}; then | |
2090 | the expansion of the %-construct will have that same text property. | |
2091 | ||
2092 | @item | |
2093 | Use a @code{(:propertize @var{elt} @var{props}@dots{})} construct to | |
2094 | give @var{elt} a text property specified by @var{props}. | |
2095 | ||
2096 | @item | |
2097 | Use a list containing @code{:eval @var{form}} in the mode-line data | |
2098 | structure, and make @var{form} evaluate to a string that has a text | |
2099 | property. | |
2100 | @end enumerate | |
2101 | ||
2102 | You can use the @code{local-map} property to specify a keymap. This | |
2103 | keymap only takes real effect for mouse clicks; binding character keys | |
2104 | and function keys to it has no effect, since it is impossible to move | |
2105 | point into the mode line. | |
2106 | ||
2107 | When the mode line refers to a variable which does not have a | |
2108 | non-@code{nil} @code{risky-local-variable} property, any text | |
2109 | properties given or specified within that variable's values are | |
2110 | ignored. This is because such properties could otherwise specify | |
2111 | functions to be called, and those functions could come from file | |
2112 | local variables. | |
2113 | ||
2114 | @node Header Lines | |
2115 | @subsection Window Header Lines | |
2116 | @cindex header line (of a window) | |
2117 | @cindex window header line | |
2118 | ||
2119 | A window can have a @dfn{header line} at the | |
2120 | top, just as it can have a mode line at the bottom. The header line | |
2121 | feature works just like the mode-line feature, except that it's | |
2122 | controlled by different variables. | |
2123 | ||
2124 | @defvar header-line-format | |
2125 | This variable, local in every buffer, specifies how to display the | |
2126 | header line, for windows displaying the buffer. The format of the value | |
2127 | is the same as for @code{mode-line-format} (@pxref{Mode Line Data}). | |
2128 | @end defvar | |
2129 | ||
2130 | @defvar default-header-line-format | |
2131 | This variable holds the default @code{header-line-format} for buffers | |
2132 | that do not override it. This is the same as @code{(default-value | |
2133 | 'header-line-format)}. | |
2134 | ||
2135 | It is normally @code{nil}, so that ordinary buffers have no header line. | |
2136 | @end defvar | |
2137 | ||
2138 | A window that is just one line tall never displays a header line. A | |
2139 | window that is two lines tall cannot display both a mode line and a | |
2140 | header line at once; if it has a mode line, then it does not display a | |
2141 | header line. | |
2142 | ||
2143 | @node Emulating Mode Line | |
2144 | @subsection Emulating Mode-Line Formatting | |
2145 | ||
2146 | You can use the function @code{format-mode-line} to compute | |
2147 | the text that would appear in a mode line or header line | |
2148 | based on a certain mode-line specification. | |
2149 | ||
2150 | @defun format-mode-line format &optional face window buffer | |
2151 | This function formats a line of text according to @var{format} as if | |
2152 | it were generating the mode line for @var{window}, but instead of | |
2153 | displaying the text in the mode line or the header line, it returns | |
2154 | the text as a string. The argument @var{window} defaults to the | |
2155 | selected window. If @var{buffer} is non-@code{nil}, all the | |
2156 | information used is taken from @var{buffer}; by default, it comes from | |
2157 | @var{window}'s buffer. | |
2158 | ||
2159 | The value string normally has text properties that correspond to the | |
2160 | faces, keymaps, etc., that the mode line would have. And any character | |
2161 | for which no @code{face} property is specified gets a default | |
2162 | value which is usually @var{face}. (If @var{face} is @code{t}, | |
2163 | that stands for either @code{mode-line} if @var{window} is selected, | |
2164 | otherwise @code{mode-line-inactive}. If @var{face} is @code{nil} or | |
2165 | omitted, that stands for no face property.) | |
2166 | ||
2167 | However, if @var{face} is an integer, the value has no text properties. | |
2168 | ||
2169 | For example, @code{(format-mode-line header-line-format)} returns the | |
2170 | text that would appear in the selected window's header line (@code{""} | |
2171 | if it has no header line). @code{(format-mode-line header-line-format | |
2172 | 'header-line)} returns the same text, with each character | |
2173 | carrying the face that it will have in the header line itself. | |
2174 | @end defun | |
2175 | ||
2176 | @node Imenu | |
2177 | @section Imenu | |
2178 | ||
2179 | @cindex Imenu | |
2180 | @dfn{Imenu} is a feature that lets users select a definition or | |
2181 | section in the buffer, from a menu which lists all of them, to go | |
2182 | directly to that location in the buffer. Imenu works by constructing | |
2183 | a buffer index which lists the names and buffer positions of the | |
2184 | definitions, or other named portions of the buffer; then the user can | |
2185 | choose one of them and move point to it. Major modes can add a menu | |
2186 | bar item to use Imenu using @code{imenu-add-to-menubar}. | |
2187 | ||
2188 | @defun imenu-add-to-menubar name | |
2189 | This function defines a local menu bar item named @var{name} | |
2190 | to run Imenu. | |
2191 | @end defun | |
2192 | ||
2193 | The user-level commands for using Imenu are described in the Emacs | |
2194 | Manual (@pxref{Imenu,, Imenu, emacs, the Emacs Manual}). This section | |
2195 | explains how to customize Imenu's method of finding definitions or | |
2196 | buffer portions for a particular major mode. | |
2197 | ||
2198 | The usual and simplest way is to set the variable | |
2199 | @code{imenu-generic-expression}: | |
2200 | ||
2201 | @defvar imenu-generic-expression | |
2202 | This variable, if non-@code{nil}, is a list that specifies regular | |
2203 | expressions for finding definitions for Imenu. Simple elements of | |
2204 | @code{imenu-generic-expression} look like this: | |
2205 | ||
2206 | @example | |
2207 | (@var{menu-title} @var{regexp} @var{index}) | |
2208 | @end example | |
2209 | ||
2210 | Here, if @var{menu-title} is non-@code{nil}, it says that the matches | |
2211 | for this element should go in a submenu of the buffer index; | |
2212 | @var{menu-title} itself specifies the name for the submenu. If | |
2213 | @var{menu-title} is @code{nil}, the matches for this element go directly | |
2214 | in the top level of the buffer index. | |
2215 | ||
2216 | The second item in the list, @var{regexp}, is a regular expression | |
2217 | (@pxref{Regular Expressions}); anything in the buffer that it matches | |
2218 | is considered a definition, something to mention in the buffer index. | |
2219 | The third item, @var{index}, is a non-negative integer that indicates | |
2220 | which subexpression in @var{regexp} matches the definition's name. | |
2221 | ||
2222 | An element can also look like this: | |
2223 | ||
2224 | @example | |
2225 | (@var{menu-title} @var{regexp} @var{index} @var{function} @var{arguments}@dots{}) | |
2226 | @end example | |
2227 | ||
2228 | Each match for this element creates an index item, and when the index | |
2229 | item is selected by the user, it calls @var{function} with arguments | |
2230 | consisting of the item name, the buffer position, and @var{arguments}. | |
2231 | ||
2232 | For Emacs Lisp mode, @code{imenu-generic-expression} could look like | |
2233 | this: | |
2234 | ||
2235 | @c should probably use imenu-syntax-alist and \\sw rather than [-A-Za-z0-9+] | |
2236 | @example | |
2237 | @group | |
2238 | ((nil "^\\s-*(def\\(un\\|subst\\|macro\\|advice\\)\ | |
2239 | \\s-+\\([-A-Za-z0-9+]+\\)" 2) | |
2240 | @end group | |
2241 | @group | |
2242 | ("*Vars*" "^\\s-*(def\\(var\\|const\\)\ | |
2243 | \\s-+\\([-A-Za-z0-9+]+\\)" 2) | |
2244 | @end group | |
2245 | @group | |
2246 | ("*Types*" | |
2247 | "^\\s-*\ | |
2248 | (def\\(type\\|struct\\|class\\|ine-condition\\)\ | |
2249 | \\s-+\\([-A-Za-z0-9+]+\\)" 2)) | |
2250 | @end group | |
2251 | @end example | |
2252 | ||
2253 | Setting this variable makes it buffer-local in the current buffer. | |
2254 | @end defvar | |
2255 | ||
2256 | @defvar imenu-case-fold-search | |
2257 | This variable controls whether matching against the regular | |
2258 | expressions in the value of @code{imenu-generic-expression} is | |
2259 | case-sensitive: @code{t}, the default, means matching should ignore | |
2260 | case. | |
2261 | ||
2262 | Setting this variable makes it buffer-local in the current buffer. | |
2263 | @end defvar | |
2264 | ||
2265 | @defvar imenu-syntax-alist | |
2266 | This variable is an alist of syntax table modifiers to use while | |
2267 | processing @code{imenu-generic-expression}, to override the syntax table | |
2268 | of the current buffer. Each element should have this form: | |
2269 | ||
2270 | @example | |
2271 | (@var{characters} . @var{syntax-description}) | |
2272 | @end example | |
2273 | ||
2274 | The @sc{car}, @var{characters}, can be either a character or a string. | |
2275 | The element says to give that character or characters the syntax | |
2276 | specified by @var{syntax-description}, which is passed to | |
2277 | @code{modify-syntax-entry} (@pxref{Syntax Table Functions}). | |
2278 | ||
2279 | This feature is typically used to give word syntax to characters which | |
2280 | normally have symbol syntax, and thus to simplify | |
2281 | @code{imenu-generic-expression} and speed up matching. | |
2282 | For example, Fortran mode uses it this way: | |
2283 | ||
2284 | @example | |
2285 | (setq imenu-syntax-alist '(("_$" . "w"))) | |
2286 | @end example | |
2287 | ||
2288 | The @code{imenu-generic-expression} regular expressions can then use | |
2289 | @samp{\\sw+} instead of @samp{\\(\\sw\\|\\s_\\)+}. Note that this | |
2290 | technique may be inconvenient when the mode needs to limit the initial | |
2291 | character of a name to a smaller set of characters than are allowed in | |
2292 | the rest of a name. | |
2293 | ||
2294 | Setting this variable makes it buffer-local in the current buffer. | |
2295 | @end defvar | |
2296 | ||
2297 | Another way to customize Imenu for a major mode is to set the | |
2298 | variables @code{imenu-prev-index-position-function} and | |
2299 | @code{imenu-extract-index-name-function}: | |
2300 | ||
2301 | @defvar imenu-prev-index-position-function | |
2302 | If this variable is non-@code{nil}, its value should be a function that | |
2303 | finds the next ``definition'' to put in the buffer index, scanning | |
2304 | backward in the buffer from point. It should return @code{nil} if it | |
2305 | doesn't find another ``definition'' before point. Otherwise it should | |
2306 | leave point at the place it finds a ``definition'' and return any | |
2307 | non-@code{nil} value. | |
2308 | ||
2309 | Setting this variable makes it buffer-local in the current buffer. | |
2310 | @end defvar | |
2311 | ||
2312 | @defvar imenu-extract-index-name-function | |
2313 | If this variable is non-@code{nil}, its value should be a function to | |
2314 | return the name for a definition, assuming point is in that definition | |
2315 | as the @code{imenu-prev-index-position-function} function would leave | |
2316 | it. | |
2317 | ||
2318 | Setting this variable makes it buffer-local in the current buffer. | |
2319 | @end defvar | |
2320 | ||
2321 | The last way to customize Imenu for a major mode is to set the | |
2322 | variable @code{imenu-create-index-function}: | |
2323 | ||
2324 | @defvar imenu-create-index-function | |
2325 | This variable specifies the function to use for creating a buffer | |
2326 | index. The function should take no arguments, and return an index | |
2327 | alist for the current buffer. It is called within | |
2328 | @code{save-excursion}, so where it leaves point makes no difference. | |
2329 | ||
2330 | The index alist can have three types of elements. Simple elements | |
2331 | look like this: | |
2332 | ||
2333 | @example | |
2334 | (@var{index-name} . @var{index-position}) | |
2335 | @end example | |
2336 | ||
2337 | Selecting a simple element has the effect of moving to position | |
2338 | @var{index-position} in the buffer. Special elements look like this: | |
2339 | ||
2340 | @example | |
2341 | (@var{index-name} @var{index-position} @var{function} @var{arguments}@dots{}) | |
2342 | @end example | |
2343 | ||
2344 | Selecting a special element performs: | |
2345 | ||
2346 | @example | |
2347 | (funcall @var{function} | |
2348 | @var{index-name} @var{index-position} @var{arguments}@dots{}) | |
2349 | @end example | |
2350 | ||
2351 | A nested sub-alist element looks like this: | |
2352 | ||
2353 | @example | |
2354 | (@var{menu-title} @var{sub-alist}) | |
2355 | @end example | |
2356 | ||
2357 | It creates the submenu @var{menu-title} specified by @var{sub-alist}. | |
2358 | ||
2359 | The default value of @code{imenu-create-index-function} is | |
2360 | @code{imenu-default-create-index-function}. This function calls the | |
2361 | value of @code{imenu-prev-index-position-function} and the value of | |
2362 | @code{imenu-extract-index-name-function} to produce the index alist. | |
2363 | However, if either of these two variables is @code{nil}, the default | |
2364 | function uses @code{imenu-generic-expression} instead. | |
2365 | ||
2366 | Setting this variable makes it buffer-local in the current buffer. | |
2367 | @end defvar | |
2368 | ||
2369 | @node Font Lock Mode | |
2370 | @section Font Lock Mode | |
2371 | @cindex Font Lock mode | |
2372 | ||
2373 | @dfn{Font Lock mode} is a feature that automatically attaches | |
2374 | @code{face} properties to certain parts of the buffer based on their | |
2375 | syntactic role. How it parses the buffer depends on the major mode; | |
2376 | most major modes define syntactic criteria for which faces to use in | |
2377 | which contexts. This section explains how to customize Font Lock for a | |
2378 | particular major mode. | |
2379 | ||
2380 | Font Lock mode finds text to highlight in two ways: through | |
2381 | syntactic parsing based on the syntax table, and through searching | |
2382 | (usually for regular expressions). Syntactic fontification happens | |
2383 | first; it finds comments and string constants and highlights them. | |
2384 | Search-based fontification happens second. | |
2385 | ||
2386 | @menu | |
2387 | * Font Lock Basics:: Overview of customizing Font Lock. | |
2388 | * Search-based Fontification:: Fontification based on regexps. | |
2389 | * Customizing Keywords:: Customizing search-based fontification. | |
2390 | * Other Font Lock Variables:: Additional customization facilities. | |
2391 | * Levels of Font Lock:: Each mode can define alternative levels | |
2392 | so that the user can select more or less. | |
2393 | * Precalculated Fontification:: How Lisp programs that produce the buffer | |
2394 | contents can also specify how to fontify it. | |
2395 | * Faces for Font Lock:: Special faces specifically for Font Lock. | |
2396 | * Syntactic Font Lock:: Fontification based on syntax tables. | |
2397 | * Setting Syntax Properties:: Defining character syntax based on context | |
2398 | using the Font Lock mechanism. | |
2399 | * Multiline Font Lock:: How to coerce Font Lock into properly | |
2400 | highlighting multiline constructs. | |
2401 | @end menu | |
2402 | ||
2403 | @node Font Lock Basics | |
2404 | @subsection Font Lock Basics | |
2405 | ||
2406 | There are several variables that control how Font Lock mode highlights | |
2407 | text. But major modes should not set any of these variables directly. | |
2408 | Instead, they should set @code{font-lock-defaults} as a buffer-local | |
2409 | variable. The value assigned to this variable is used, if and when Font | |
2410 | Lock mode is enabled, to set all the other variables. | |
2411 | ||
2412 | @defvar font-lock-defaults | |
2413 | This variable is set by major modes, as a buffer-local variable, to | |
2414 | specify how to fontify text in that mode. It automatically becomes | |
2415 | buffer-local when you set it. If its value is @code{nil}, Font-Lock | |
2416 | mode does no highlighting, and you can use the @samp{Faces} menu | |
2417 | (under @samp{Edit} and then @samp{Text Properties} in the menu bar) to | |
2418 | assign faces explicitly to text in the buffer. | |
2419 | ||
2420 | If non-@code{nil}, the value should look like this: | |
2421 | ||
2422 | @example | |
2423 | (@var{keywords} [@var{keywords-only} [@var{case-fold} | |
2424 | [@var{syntax-alist} [@var{syntax-begin} @var{other-vars}@dots{}]]]]) | |
2425 | @end example | |
2426 | ||
2427 | The first element, @var{keywords}, indirectly specifies the value of | |
2428 | @code{font-lock-keywords} which directs search-based fontification. | |
2429 | It can be a symbol, a variable or a function whose value is the list | |
2430 | to use for @code{font-lock-keywords}. It can also be a list of | |
2431 | several such symbols, one for each possible level of fontification. | |
2432 | The first symbol specifies how to do level 1 fontification, the second | |
2433 | symbol how to do level 2, and so on. @xref{Levels of Font Lock}. | |
2434 | ||
2435 | The second element, @var{keywords-only}, specifies the value of the | |
2436 | variable @code{font-lock-keywords-only}. If this is omitted or | |
2437 | @code{nil}, syntactic fontification (of strings and comments) is also | |
2438 | performed. If this is non-@code{nil}, such fontification is not | |
2439 | performed. @xref{Syntactic Font Lock}. | |
2440 | ||
2441 | The third element, @var{case-fold}, specifies the value of | |
2442 | @code{font-lock-keywords-case-fold-search}. If it is non-@code{nil}, | |
2443 | Font Lock mode ignores case when searching as directed by | |
2444 | @code{font-lock-keywords}. | |
2445 | ||
2446 | If the fourth element, @var{syntax-alist}, is non-@code{nil}, it | |
2447 | should be a list of cons cells of the form @code{(@var{char-or-string} | |
2448 | . @var{string})}. These are used to set up a syntax table for | |
2449 | syntactic fontification (@pxref{Syntax Table Functions}). The | |
2450 | resulting syntax table is stored in @code{font-lock-syntax-table}. | |
2451 | ||
2452 | The fifth element, @var{syntax-begin}, specifies the value of | |
2453 | @code{font-lock-beginning-of-syntax-function}. We recommend setting | |
2454 | this variable to @code{nil} and using @code{syntax-begin-function} | |
2455 | instead. | |
2456 | ||
2457 | All the remaining elements (if any) are collectively called | |
2458 | @var{other-vars}. Each of these elements should have the form | |
2459 | @code{(@var{variable} . @var{value})}---which means, make | |
2460 | @var{variable} buffer-local and then set it to @var{value}. You can | |
2461 | use these @var{other-vars} to set other variables that affect | |
2462 | fontification, aside from those you can control with the first five | |
2463 | elements. @xref{Other Font Lock Variables}. | |
2464 | @end defvar | |
2465 | ||
2466 | If your mode fontifies text explicitly by adding | |
2467 | @code{font-lock-face} properties, it can specify @code{(nil t)} for | |
2468 | @code{font-lock-defaults} to turn off all automatic fontification. | |
2469 | However, this is not required; it is possible to fontify some things | |
2470 | using @code{font-lock-face} properties and set up automatic | |
2471 | fontification for other parts of the text. | |
2472 | ||
2473 | @node Search-based Fontification | |
2474 | @subsection Search-based Fontification | |
2475 | ||
2476 | The most important variable for customizing Font Lock mode is | |
2477 | @code{font-lock-keywords}. It specifies the search criteria for | |
2478 | search-based fontification. You should specify the value of this | |
2479 | variable with @var{keywords} in @code{font-lock-defaults}. | |
2480 | ||
2481 | @defvar font-lock-keywords | |
2482 | This variable's value is a list of the keywords to highlight. Be | |
2483 | careful when composing regular expressions for this list; a poorly | |
2484 | written pattern can dramatically slow things down! | |
2485 | @end defvar | |
2486 | ||
2487 | Each element of @code{font-lock-keywords} specifies how to find | |
2488 | certain cases of text, and how to highlight those cases. Font Lock mode | |
2489 | processes the elements of @code{font-lock-keywords} one by one, and for | |
2490 | each element, it finds and handles all matches. Ordinarily, once | |
2491 | part of the text has been fontified already, this cannot be overridden | |
2492 | by a subsequent match in the same text; but you can specify different | |
2493 | behavior using the @var{override} element of a @var{subexp-highlighter}. | |
2494 | ||
2495 | Each element of @code{font-lock-keywords} should have one of these | |
2496 | forms: | |
2497 | ||
2498 | @table @code | |
2499 | @item @var{regexp} | |
2500 | Highlight all matches for @var{regexp} using | |
2501 | @code{font-lock-keyword-face}. For example, | |
2502 | ||
2503 | @example | |
2504 | ;; @r{Highlight occurrences of the word @samp{foo}} | |
2505 | ;; @r{using @code{font-lock-keyword-face}.} | |
2506 | "\\<foo\\>" | |
2507 | @end example | |
2508 | ||
2509 | The function @code{regexp-opt} (@pxref{Regexp Functions}) is useful | |
2510 | for calculating optimal regular expressions to match a number of | |
2511 | different keywords. | |
2512 | ||
2513 | @item @var{function} | |
2514 | Find text by calling @var{function}, and highlight the matches | |
2515 | it finds using @code{font-lock-keyword-face}. | |
2516 | ||
2517 | When @var{function} is called, it receives one argument, the limit of | |
2518 | the search; it should begin searching at point, and not search beyond the | |
2519 | limit. It should return non-@code{nil} if it succeeds, and set the | |
2520 | match data to describe the match that was found. Returning @code{nil} | |
2521 | indicates failure of the search. | |
2522 | ||
2523 | Fontification will call @var{function} repeatedly with the same limit, | |
2524 | and with point where the previous invocation left it, until | |
2525 | @var{function} fails. On failure, @var{function} need not reset point | |
2526 | in any particular way. | |
2527 | ||
2528 | @item (@var{matcher} . @var{subexp}) | |
2529 | In this kind of element, @var{matcher} is either a regular | |
2530 | expression or a function, as described above. The @sc{cdr}, | |
2531 | @var{subexp}, specifies which subexpression of @var{matcher} should be | |
2532 | highlighted (instead of the entire text that @var{matcher} matched). | |
2533 | ||
2534 | @example | |
2535 | ;; @r{Highlight the @samp{bar} in each occurrence of @samp{fubar},} | |
2536 | ;; @r{using @code{font-lock-keyword-face}.} | |
2537 | ("fu\\(bar\\)" . 1) | |
2538 | @end example | |
2539 | ||
2540 | If you use @code{regexp-opt} to produce the regular expression | |
2541 | @var{matcher}, you can use @code{regexp-opt-depth} (@pxref{Regexp | |
2542 | Functions}) to calculate the value for @var{subexp}. | |
2543 | ||
2544 | @item (@var{matcher} . @var{facespec}) | |
2545 | In this kind of element, @var{facespec} is an expression whose value | |
2546 | specifies the face to use for highlighting. In the simplest case, | |
2547 | @var{facespec} is a Lisp variable (a symbol) whose value is a face | |
2548 | name. | |
2549 | ||
2550 | @example | |
2551 | ;; @r{Highlight occurrences of @samp{fubar},} | |
2552 | ;; @r{using the face which is the value of @code{fubar-face}.} | |
2553 | ("fubar" . fubar-face) | |
2554 | @end example | |
2555 | ||
2556 | However, @var{facespec} can also evaluate to a list of this form: | |
2557 | ||
2558 | @example | |
2559 | (face @var{face} @var{prop1} @var{val1} @var{prop2} @var{val2}@dots{}) | |
2560 | @end example | |
2561 | ||
2562 | @noindent | |
2563 | to specify the face @var{face} and various additional text properties | |
2564 | to put on the text that matches. If you do this, be sure to add the | |
2565 | other text property names that you set in this way to the value of | |
2566 | @code{font-lock-extra-managed-props} so that the properties will also | |
2567 | be cleared out when they are no longer appropriate. Alternatively, | |
2568 | you can set the variable @code{font-lock-unfontify-region-function} to | |
2569 | a function that clears these properties. @xref{Other Font Lock | |
2570 | Variables}. | |
2571 | ||
2572 | @item (@var{matcher} . @var{subexp-highlighter}) | |
2573 | In this kind of element, @var{subexp-highlighter} is a list | |
2574 | which specifies how to highlight matches found by @var{matcher}. | |
2575 | It has the form: | |
2576 | ||
2577 | @example | |
2578 | (@var{subexp} @var{facespec} [[@var{override} [@var{laxmatch}]]) | |
2579 | @end example | |
2580 | ||
2581 | The @sc{car}, @var{subexp}, is an integer specifying which subexpression | |
2582 | of the match to fontify (0 means the entire matching text). The second | |
2583 | subelement, @var{facespec}, is an expression whose value specifies the | |
2584 | face, as described above. | |
2585 | ||
2586 | The last two values in @var{subexp-highlighter}, @var{override} and | |
2587 | @var{laxmatch}, are optional flags. If @var{override} is @code{t}, | |
2588 | this element can override existing fontification made by previous | |
2589 | elements of @code{font-lock-keywords}. If it is @code{keep}, then | |
2590 | each character is fontified if it has not been fontified already by | |
2591 | some other element. If it is @code{prepend}, the face specified by | |
2592 | @var{facespec} is added to the beginning of the @code{font-lock-face} | |
2593 | property. If it is @code{append}, the face is added to the end of the | |
2594 | @code{font-lock-face} property. | |
2595 | ||
2596 | If @var{laxmatch} is non-@code{nil}, it means there should be no error | |
2597 | if there is no subexpression numbered @var{subexp} in @var{matcher}. | |
2598 | Obviously, fontification of the subexpression numbered @var{subexp} will | |
2599 | not occur. However, fontification of other subexpressions (and other | |
2600 | regexps) will continue. If @var{laxmatch} is @code{nil}, and the | |
2601 | specified subexpression is missing, then an error is signaled which | |
2602 | terminates search-based fontification. | |
2603 | ||
2604 | Here are some examples of elements of this kind, and what they do: | |
2605 | ||
2606 | @smallexample | |
2607 | ;; @r{Highlight occurrences of either @samp{foo} or @samp{bar}, using} | |
2608 | ;; @r{@code{foo-bar-face}, even if they have already been highlighted.} | |
2609 | ;; @r{@code{foo-bar-face} should be a variable whose value is a face.} | |
2610 | ("foo\\|bar" 0 foo-bar-face t) | |
2611 | ||
2612 | ;; @r{Highlight the first subexpression within each occurrence} | |
2613 | ;; @r{that the function @code{fubar-match} finds,} | |
2614 | ;; @r{using the face which is the value of @code{fubar-face}.} | |
2615 | (fubar-match 1 fubar-face) | |
2616 | @end smallexample | |
2617 | ||
2618 | @item (@var{matcher} . @var{anchored-highlighter}) | |
2619 | In this kind of element, @var{anchored-highlighter} specifies how to | |
2620 | highlight text that follows a match found by @var{matcher}. So a | |
2621 | match found by @var{matcher} acts as the anchor for further searches | |
2622 | specified by @var{anchored-highlighter}. @var{anchored-highlighter} | |
2623 | is a list of the following form: | |
2624 | ||
2625 | @example | |
2626 | (@var{anchored-matcher} @var{pre-form} @var{post-form} | |
2627 | @var{subexp-highlighters}@dots{}) | |
2628 | @end example | |
2629 | ||
2630 | Here, @var{anchored-matcher}, like @var{matcher}, is either a regular | |
2631 | expression or a function. After a match of @var{matcher} is found, | |
2632 | point is at the end of the match. Now, Font Lock evaluates the form | |
2633 | @var{pre-form}. Then it searches for matches of | |
2634 | @var{anchored-matcher} and uses @var{subexp-highlighters} to highlight | |
2635 | these. A @var{subexp-highlighter} is as described above. Finally, | |
2636 | Font Lock evaluates @var{post-form}. | |
2637 | ||
2638 | The forms @var{pre-form} and @var{post-form} can be used to initialize | |
2639 | before, and cleanup after, @var{anchored-matcher} is used. Typically, | |
2640 | @var{pre-form} is used to move point to some position relative to the | |
2641 | match of @var{matcher}, before starting with @var{anchored-matcher}. | |
2642 | @var{post-form} might be used to move back, before resuming with | |
2643 | @var{matcher}. | |
2644 | ||
2645 | After Font Lock evaluates @var{pre-form}, it does not search for | |
2646 | @var{anchored-matcher} beyond the end of the line. However, if | |
2647 | @var{pre-form} returns a buffer position that is greater than the | |
2648 | position of point after @var{pre-form} is evaluated, then the position | |
2649 | returned by @var{pre-form} is used as the limit of the search instead. | |
2650 | It is generally a bad idea to return a position greater than the end | |
2651 | of the line; in other words, the @var{anchored-matcher} search should | |
2652 | not span lines. | |
2653 | ||
2654 | For example, | |
2655 | ||
2656 | @smallexample | |
2657 | ;; @r{Highlight occurrences of the word @samp{item} following} | |
2658 | ;; @r{an occurrence of the word @samp{anchor} (on the same line)} | |
2659 | ;; @r{in the value of @code{item-face}.} | |
2660 | ("\\<anchor\\>" "\\<item\\>" nil nil (0 item-face)) | |
2661 | @end smallexample | |
2662 | ||
2663 | Here, @var{pre-form} and @var{post-form} are @code{nil}. Therefore | |
2664 | searching for @samp{item} starts at the end of the match of | |
2665 | @samp{anchor}, and searching for subsequent instances of @samp{anchor} | |
2666 | resumes from where searching for @samp{item} concluded. | |
2667 | ||
2668 | @item (@var{matcher} @var{highlighters}@dots{}) | |
2669 | This sort of element specifies several @var{highlighter} lists for a | |
2670 | single @var{matcher}. A @var{highlighter} list can be of the type | |
2671 | @var{subexp-highlighter} or @var{anchored-highlighter} as described | |
2672 | above. | |
2673 | ||
2674 | For example, | |
2675 | ||
2676 | @smallexample | |
2677 | ;; @r{Highlight occurrences of the word @samp{anchor} in the value} | |
2678 | ;; @r{of @code{anchor-face}, and subsequent occurrences of the word} | |
2679 | ;; @r{@samp{item} (on the same line) in the value of @code{item-face}.} | |
2680 | ("\\<anchor\\>" (0 anchor-face) | |
2681 | ("\\<item\\>" nil nil (0 item-face))) | |
2682 | @end smallexample | |
2683 | ||
2684 | @item (eval . @var{form}) | |
2685 | Here @var{form} is an expression to be evaluated the first time | |
2686 | this value of @code{font-lock-keywords} is used in a buffer. | |
2687 | Its value should have one of the forms described in this table. | |
2688 | @end table | |
2689 | ||
2690 | @strong{Warning:} Do not design an element of @code{font-lock-keywords} | |
2691 | to match text which spans lines; this does not work reliably. | |
2692 | For details, see @xref{Multiline Font Lock}. | |
2693 | ||
2694 | You can use @var{case-fold} in @code{font-lock-defaults} to specify | |
2695 | the value of @code{font-lock-keywords-case-fold-search} which says | |
2696 | whether search-based fontification should be case-insensitive. | |
2697 | ||
2698 | @defvar font-lock-keywords-case-fold-search | |
2699 | Non-@code{nil} means that regular expression matching for the sake of | |
2700 | @code{font-lock-keywords} should be case-insensitive. | |
2701 | @end defvar | |
2702 | ||
2703 | @node Customizing Keywords | |
2704 | @subsection Customizing Search-Based Fontification | |
2705 | ||
2706 | You can use @code{font-lock-add-keywords} to add additional | |
2707 | search-based fontification rules to a major mode, and | |
2708 | @code{font-lock-remove-keywords} to removes rules. | |
2709 | ||
2710 | @defun font-lock-add-keywords mode keywords &optional how | |
2711 | This function adds highlighting @var{keywords}, for the current buffer | |
2712 | or for major mode @var{mode}. The argument @var{keywords} should be a | |
2713 | list with the same format as the variable @code{font-lock-keywords}. | |
2714 | ||
2715 | If @var{mode} is a symbol which is a major mode command name, such as | |
2716 | @code{c-mode}, the effect is that enabling Font Lock mode in | |
2717 | @var{mode} will add @var{keywords} to @code{font-lock-keywords}. | |
2718 | Calling with a non-@code{nil} value of @var{mode} is correct only in | |
2719 | your @file{~/.emacs} file. | |
2720 | ||
2721 | If @var{mode} is @code{nil}, this function adds @var{keywords} to | |
2722 | @code{font-lock-keywords} in the current buffer. This way of calling | |
2723 | @code{font-lock-add-keywords} is usually used in mode hook functions. | |
2724 | ||
2725 | By default, @var{keywords} are added at the beginning of | |
2726 | @code{font-lock-keywords}. If the optional argument @var{how} is | |
2727 | @code{set}, they are used to replace the value of | |
2728 | @code{font-lock-keywords}. If @var{how} is any other non-@code{nil} | |
2729 | value, they are added at the end of @code{font-lock-keywords}. | |
2730 | ||
2731 | Some modes provide specialized support you can use in additional | |
2732 | highlighting patterns. See the variables | |
2733 | @code{c-font-lock-extra-types}, @code{c++-font-lock-extra-types}, | |
2734 | and @code{java-font-lock-extra-types}, for example. | |
2735 | ||
2736 | @strong{Warning:} major mode functions must not call | |
2737 | @code{font-lock-add-keywords} under any circumstances, either directly | |
2738 | or indirectly, except through their mode hooks. (Doing so would lead | |
2739 | to incorrect behavior for some minor modes.) They should set up their | |
2740 | rules for search-based fontification by setting | |
2741 | @code{font-lock-keywords}. | |
2742 | @end defun | |
2743 | ||
2744 | @defun font-lock-remove-keywords mode keywords | |
2745 | This function removes @var{keywords} from @code{font-lock-keywords} | |
2746 | for the current buffer or for major mode @var{mode}. As in | |
2747 | @code{font-lock-add-keywords}, @var{mode} should be a major mode | |
2748 | command name or @code{nil}. All the caveats and requirements for | |
2749 | @code{font-lock-add-keywords} apply here too. | |
2750 | @end defun | |
2751 | ||
2752 | For example, this code | |
2753 | ||
2754 | @smallexample | |
2755 | (font-lock-add-keywords 'c-mode | |
2756 | '(("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend) | |
2757 | ("\\<\\(and\\|or\\|not\\)\\>" . font-lock-keyword-face))) | |
2758 | @end smallexample | |
2759 | ||
2760 | @noindent | |
2761 | adds two fontification patterns for C mode: one to fontify the word | |
2762 | @samp{FIXME}, even in comments, and another to fontify the words | |
2763 | @samp{and}, @samp{or} and @samp{not} as keywords. | |
2764 | ||
2765 | @noindent | |
2766 | That example affects only C mode proper. To add the same patterns to | |
2767 | C mode @emph{and} all modes derived from it, do this instead: | |
2768 | ||
2769 | @smallexample | |
2770 | (add-hook 'c-mode-hook | |
2771 | (lambda () | |
2772 | (font-lock-add-keywords nil | |
2773 | '(("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend) | |
2774 | ("\\<\\(and\\|or\\|not\\)\\>" . | |
2775 | font-lock-keyword-face))))) | |
2776 | @end smallexample | |
2777 | ||
2778 | @node Other Font Lock Variables | |
2779 | @subsection Other Font Lock Variables | |
2780 | ||
2781 | This section describes additional variables that a major mode can | |
2782 | set by means of @var{other-vars} in @code{font-lock-defaults} | |
2783 | (@pxref{Font Lock Basics}). | |
2784 | ||
2785 | @defvar font-lock-mark-block-function | |
2786 | If this variable is non-@code{nil}, it should be a function that is | |
2787 | called with no arguments, to choose an enclosing range of text for | |
2788 | refontification for the command @kbd{M-o M-o} | |
2789 | (@code{font-lock-fontify-block}). | |
2790 | ||
2791 | The function should report its choice by placing the region around it. | |
2792 | A good choice is a range of text large enough to give proper results, | |
2793 | but not too large so that refontification becomes slow. Typical values | |
2794 | are @code{mark-defun} for programming modes or @code{mark-paragraph} for | |
2795 | textual modes. | |
2796 | @end defvar | |
2797 | ||
2798 | @defvar font-lock-extra-managed-props | |
2799 | This variable specifies additional properties (other than | |
2800 | @code{font-lock-face}) that are being managed by Font Lock mode. It | |
2801 | is used by @code{font-lock-default-unfontify-region}, which normally | |
2802 | only manages the @code{font-lock-face} property. If you want Font | |
2803 | Lock to manage other properties as well, you must specify them in a | |
2804 | @var{facespec} in @code{font-lock-keywords} as well as add them to | |
2805 | this list. @xref{Search-based Fontification}. | |
2806 | @end defvar | |
2807 | ||
2808 | @defvar font-lock-fontify-buffer-function | |
2809 | Function to use for fontifying the buffer. The default value is | |
2810 | @code{font-lock-default-fontify-buffer}. | |
2811 | @end defvar | |
2812 | ||
2813 | @defvar font-lock-unfontify-buffer-function | |
2814 | Function to use for unfontifying the buffer. This is used when | |
2815 | turning off Font Lock mode. The default value is | |
2816 | @code{font-lock-default-unfontify-buffer}. | |
2817 | @end defvar | |
2818 | ||
2819 | @defvar font-lock-fontify-region-function | |
2820 | Function to use for fontifying a region. It should take two | |
2821 | arguments, the beginning and end of the region, and an optional third | |
2822 | argument @var{verbose}. If @var{verbose} is non-@code{nil}, the | |
2823 | function should print status messages. The default value is | |
2824 | @code{font-lock-default-fontify-region}. | |
2825 | @end defvar | |
2826 | ||
2827 | @defvar font-lock-unfontify-region-function | |
2828 | Function to use for unfontifying a region. It should take two | |
2829 | arguments, the beginning and end of the region. The default value is | |
2830 | @code{font-lock-default-unfontify-region}. | |
2831 | @end defvar | |
2832 | ||
2833 | @ignore | |
2834 | @defvar font-lock-inhibit-thing-lock | |
2835 | List of Font Lock mode related modes that should not be turned on. | |
2836 | Currently, valid mode names are @code{fast-lock-mode}, | |
2837 | @code{jit-lock-mode} and @code{lazy-lock-mode}. | |
2838 | @end defvar | |
2839 | @end ignore | |
2840 | ||
2841 | @node Levels of Font Lock | |
2842 | @subsection Levels of Font Lock | |
2843 | ||
2844 | Many major modes offer three different levels of fontification. You | |
2845 | can define multiple levels by using a list of symbols for @var{keywords} | |
2846 | in @code{font-lock-defaults}. Each symbol specifies one level of | |
2847 | fontification; it is up to the user to choose one of these levels. The | |
2848 | chosen level's symbol value is used to initialize | |
2849 | @code{font-lock-keywords}. | |
2850 | ||
2851 | Here are the conventions for how to define the levels of | |
2852 | fontification: | |
2853 | ||
2854 | @itemize @bullet | |
2855 | @item | |
2856 | Level 1: highlight function declarations, file directives (such as include or | |
2857 | import directives), strings and comments. The idea is speed, so only | |
2858 | the most important and top-level components are fontified. | |
2859 | ||
2860 | @item | |
2861 | Level 2: in addition to level 1, highlight all language keywords, | |
2862 | including type names that act like keywords, as well as named constant | |
2863 | values. The idea is that all keywords (either syntactic or semantic) | |
2864 | should be fontified appropriately. | |
2865 | ||
2866 | @item | |
2867 | Level 3: in addition to level 2, highlight the symbols being defined in | |
2868 | function and variable declarations, and all builtin function names, | |
2869 | wherever they appear. | |
2870 | @end itemize | |
2871 | ||
2872 | @node Precalculated Fontification | |
2873 | @subsection Precalculated Fontification | |
2874 | ||
2875 | In addition to using @code{font-lock-defaults} for search-based | |
2876 | fontification, you may use the special character property | |
2877 | @code{font-lock-face} (@pxref{Special Properties}). This property | |
2878 | acts just like the explicit @code{face} property, but its activation | |
2879 | is toggled when the user calls @kbd{M-x font-lock-mode}. Using | |
2880 | @code{font-lock-face} is especially convenient for special modes | |
2881 | which construct their text programmatically, such as | |
2882 | @code{list-buffers} and @code{occur}. | |
2883 | ||
2884 | If your mode does not use any of the other machinery of Font Lock | |
2885 | (i.e. it only uses the @code{font-lock-face} property), it should not | |
2886 | set the variable @code{font-lock-defaults}. | |
2887 | ||
2888 | @node Faces for Font Lock | |
2889 | @subsection Faces for Font Lock | |
2890 | @cindex faces for font lock | |
2891 | @cindex font lock faces | |
2892 | ||
2893 | You can make Font Lock mode use any face, but several faces are | |
2894 | defined specifically for Font Lock mode. Each of these symbols is both | |
2895 | a face name, and a variable whose default value is the symbol itself. | |
2896 | Thus, the default value of @code{font-lock-comment-face} is | |
2897 | @code{font-lock-comment-face}. This means you can write | |
2898 | @code{font-lock-comment-face} in a context such as | |
2899 | @code{font-lock-keywords} where a face-name-valued expression is used. | |
2900 | ||
2901 | @table @code | |
2902 | @item font-lock-comment-face | |
2903 | @vindex font-lock-comment-face | |
2904 | Used (typically) for comments. | |
2905 | ||
2906 | @item font-lock-comment-delimiter-face | |
2907 | @vindex font-lock-comment-delimiter-face | |
2908 | Used (typically) for comments delimiters. | |
2909 | ||
2910 | @item font-lock-doc-face | |
2911 | @vindex font-lock-doc-face | |
2912 | Used (typically) for documentation strings in the code. | |
2913 | ||
2914 | @item font-lock-string-face | |
2915 | @vindex font-lock-string-face | |
2916 | Used (typically) for string constants. | |
2917 | ||
2918 | @item font-lock-keyword-face | |
2919 | @vindex font-lock-keyword-face | |
2920 | Used (typically) for keywords---names that have special syntactic | |
2921 | significance, like @code{for} and @code{if} in C. | |
2922 | ||
2923 | @item font-lock-builtin-face | |
2924 | @vindex font-lock-builtin-face | |
2925 | Used (typically) for built-in function names. | |
2926 | ||
2927 | @item font-lock-function-name-face | |
2928 | @vindex font-lock-function-name-face | |
2929 | Used (typically) for the name of a function being defined or declared, | |
2930 | in a function definition or declaration. | |
2931 | ||
2932 | @item font-lock-variable-name-face | |
2933 | @vindex font-lock-variable-name-face | |
2934 | Used (typically) for the name of a variable being defined or declared, | |
2935 | in a variable definition or declaration. | |
2936 | ||
2937 | @item font-lock-type-face | |
2938 | @vindex font-lock-type-face | |
2939 | Used (typically) for names of user-defined data types, | |
2940 | where they are defined and where they are used. | |
2941 | ||
2942 | @item font-lock-constant-face | |
2943 | @vindex font-lock-constant-face | |
2944 | Used (typically) for constant names. | |
2945 | ||
2946 | @item font-lock-preprocessor-face | |
2947 | @vindex font-lock-preprocessor-face | |
2948 | Used (typically) for preprocessor commands. | |
2949 | ||
2950 | @item font-lock-negation-char-face | |
2951 | @vindex font-lock-negation-char-face | |
2952 | Used (typically) for easily-overlooked negation characters. | |
2953 | ||
2954 | @item font-lock-warning-face | |
2955 | @vindex font-lock-warning-face | |
2956 | Used (typically) for constructs that are peculiar, or that greatly | |
2957 | change the meaning of other text. For example, this is used for | |
2958 | @samp{;;;###autoload} cookies in Emacs Lisp, and for @code{#error} | |
2959 | directives in C. | |
2960 | @end table | |
2961 | ||
2962 | @node Syntactic Font Lock | |
2963 | @subsection Syntactic Font Lock | |
2964 | @cindex syntactic font lock | |
2965 | ||
2966 | Syntactic fontification uses the syntax table to find comments and | |
2967 | string constants (@pxref{Syntax Tables}). It highlights them using | |
2968 | @code{font-lock-comment-face} and @code{font-lock-string-face} | |
2969 | (@pxref{Faces for Font Lock}), or whatever | |
2970 | @code{font-lock-syntactic-face-function} chooses. There are several | |
2971 | variables that affect syntactic fontification; you should set them by | |
2972 | means of @code{font-lock-defaults} (@pxref{Font Lock Basics}). | |
2973 | ||
2974 | @defvar font-lock-keywords-only | |
2975 | Non-@code{nil} means Font Lock should not do syntactic fontification; | |
2976 | it should only fontify based on @code{font-lock-keywords}. The normal | |
2977 | way for a mode to set this variable to @code{t} is with | |
2978 | @var{keywords-only} in @code{font-lock-defaults}. | |
2979 | @end defvar | |
2980 | ||
2981 | @defvar font-lock-syntax-table | |
2982 | This variable holds the syntax table to use for fontification of | |
2983 | comments and strings. Specify it using @var{syntax-alist} in | |
2984 | @code{font-lock-defaults}. If this is @code{nil}, fontification uses | |
2985 | the buffer's syntax table. | |
2986 | @end defvar | |
2987 | ||
2988 | @defvar font-lock-beginning-of-syntax-function | |
2989 | If this variable is non-@code{nil}, it should be a function to move | |
2990 | point back to a position that is syntactically at ``top level'' and | |
2991 | outside of strings or comments. Font Lock uses this when necessary | |
2992 | to get the right results for syntactic fontification. | |
2993 | ||
2994 | This function is called with no arguments. It should leave point at | |
2995 | the beginning of any enclosing syntactic block. Typical values are | |
2996 | @code{beginning-of-line} (used when the start of the line is known to | |
2997 | be outside a syntactic block), or @code{beginning-of-defun} for | |
2998 | programming modes, or @code{backward-paragraph} for textual modes. | |
2999 | ||
3000 | If the value is @code{nil}, Font Lock uses | |
3001 | @code{syntax-begin-function} to move back outside of any comment, | |
3002 | string, or sexp. This variable is semi-obsolete; we recommend setting | |
3003 | @code{syntax-begin-function} instead. | |
3004 | ||
3005 | Specify this variable using @var{syntax-begin} in | |
3006 | @code{font-lock-defaults}. | |
3007 | @end defvar | |
3008 | ||
3009 | @defvar font-lock-syntactic-face-function | |
3010 | A function to determine which face to use for a given syntactic | |
3011 | element (a string or a comment). The function is called with one | |
3012 | argument, the parse state at point returned by | |
3013 | @code{parse-partial-sexp}, and should return a face. The default | |
3014 | value returns @code{font-lock-comment-face} for comments and | |
3015 | @code{font-lock-string-face} for strings. | |
3016 | ||
3017 | This can be used to highlighting different kinds of strings or | |
3018 | comments differently. It is also sometimes abused together with | |
3019 | @code{font-lock-syntactic-keywords} to highlight constructs that span | |
3020 | multiple lines, but this is too esoteric to document here. | |
3021 | ||
3022 | Specify this variable using @var{other-vars} in | |
3023 | @code{font-lock-defaults}. | |
3024 | @end defvar | |
3025 | ||
3026 | @node Setting Syntax Properties | |
3027 | @subsection Setting Syntax Properties | |
3028 | ||
3029 | Font Lock mode can be used to update @code{syntax-table} properties | |
3030 | automatically (@pxref{Syntax Properties}). This is useful in | |
3031 | languages for which a single syntax table by itself is not sufficient. | |
3032 | ||
3033 | @defvar font-lock-syntactic-keywords | |
3034 | This variable enables and controls updating @code{syntax-table} | |
3035 | properties by Font Lock. Its value should be a list of elements of | |
3036 | this form: | |
3037 | ||
3038 | @example | |
3039 | (@var{matcher} @var{subexp} @var{syntax} @var{override} @var{laxmatch}) | |
3040 | @end example | |
3041 | ||
3042 | The parts of this element have the same meanings as in the corresponding | |
3043 | sort of element of @code{font-lock-keywords}, | |
3044 | ||
3045 | @example | |
3046 | (@var{matcher} @var{subexp} @var{facespec} @var{override} @var{laxmatch}) | |
3047 | @end example | |
3048 | ||
3049 | However, instead of specifying the value @var{facespec} to use for the | |
3050 | @code{face} property, it specifies the value @var{syntax} to use for | |
3051 | the @code{syntax-table} property. Here, @var{syntax} can be a string | |
3052 | (as taken by @code{modify-syntax-entry}), a syntax table, a cons cell | |
3053 | (as returned by @code{string-to-syntax}), or an expression whose value | |
3054 | is one of those two types. @var{override} cannot be @code{prepend} or | |
3055 | @code{append}. | |
3056 | ||
3057 | For example, an element of the form: | |
3058 | ||
3059 | @example | |
3060 | ("\\$\\(#\\)" 1 ".") | |
3061 | @end example | |
3062 | ||
3063 | highlights syntactically a hash character when following a dollar | |
3064 | character, with a SYNTAX of @code{"."} (meaning punctuation syntax). | |
3065 | Assuming that the buffer syntax table specifies hash characters to | |
3066 | have comment start syntax, the element will only highlight hash | |
3067 | characters that do not follow dollar characters as comments | |
3068 | syntactically. | |
3069 | ||
3070 | An element of the form: | |
3071 | ||
3072 | @example | |
3073 | ("\\('\\).\\('\\)" | |
3074 | (1 "\"") | |
3075 | (2 "\"")) | |
3076 | @end example | |
3077 | ||
3078 | highlights syntactically both single quotes which surround a single | |
3079 | character, with a SYNTAX of @code{"\""} (meaning string quote syntax). | |
3080 | Assuming that the buffer syntax table does not specify single quotes | |
3081 | to have quote syntax, the element will only highlight single quotes of | |
3082 | the form @samp{'@var{c}'} as strings syntactically. Other forms, such | |
3083 | as @samp{foo'bar} or @samp{'fubar'}, will not be highlighted as | |
3084 | strings. | |
3085 | ||
3086 | Major modes normally set this variable with @var{other-vars} in | |
3087 | @code{font-lock-defaults}. | |
3088 | @end defvar | |
3089 | ||
3090 | @node Multiline Font Lock | |
3091 | @subsection Multiline Font Lock Constructs | |
3092 | @cindex multiline font lock | |
3093 | ||
3094 | Normally, elements of @code{font-lock-keywords} should not match | |
3095 | across multiple lines; that doesn't work reliably, because Font Lock | |
3096 | usually scans just part of the buffer, and it can miss a multi-line | |
3097 | construct that crosses the line boundary where the scan starts. (The | |
3098 | scan normally starts at the beginning of a line.) | |
3099 | ||
3100 | Making elements that match multiline constructs work properly has | |
3101 | two aspects: correct @emph{identification} and correct | |
3102 | @emph{rehighlighting}. The first means that Font Lock finds all | |
3103 | multiline constructs. The second means that Font Lock will correctly | |
3104 | rehighlight all the relevant text when a multiline construct is | |
3105 | changed---for example, if some of the text that was previously part of | |
3106 | a multiline construct ceases to be part of it. The two aspects are | |
3107 | closely related, and often getting one of them to work will appear to | |
3108 | make the other also work. However, for reliable results you must | |
3109 | attend explicitly to both aspects. | |
3110 | ||
3111 | There are three ways to ensure correct identification of multiline | |
3112 | constructs: | |
3113 | ||
3114 | @itemize | |
3115 | @item | |
3116 | Add a function to @code{font-lock-extend-region-functions} that does | |
3117 | the @emph{identification} and extends the scan so that the scanned | |
3118 | text never starts or ends in the middle of a multiline construct. | |
3119 | @item | |
3120 | Use the @code{font-lock-fontify-region-function} hook similarly to | |
3121 | extend the scan so that the scanned text never starts or ends in the | |
3122 | middle of a multiline construct. | |
3123 | @item | |
3124 | Somehow identify the multiline construct right when it gets inserted | |
3125 | into the buffer (or at any point after that but before font-lock | |
3126 | tries to highlight it), and mark it with a @code{font-lock-multiline} | |
3127 | which will instruct font-lock not to start or end the scan in the | |
3128 | middle of the construct. | |
3129 | @end itemize | |
3130 | ||
3131 | There are three ways to do rehighlighting of multiline constructs: | |
3132 | ||
3133 | @itemize | |
3134 | @item | |
3135 | Place a @code{font-lock-multiline} property on the construct. This | |
3136 | will rehighlight the whole construct if any part of it is changed. In | |
3137 | some cases you can do this automatically by setting the | |
3138 | @code{font-lock-multiline} variable, which see. | |
3139 | @item | |
3140 | Make sure @code{jit-lock-contextually} is set and rely on it doing its | |
3141 | job. This will only rehighlight the part of the construct that | |
3142 | follows the actual change, and will do it after a short delay. | |
3143 | This only works if the highlighting of the various parts of your | |
3144 | multiline construct never depends on text in subsequent lines. | |
3145 | Since @code{jit-lock-contextually} is activated by default, this can | |
3146 | be an attractive solution. | |
3147 | @item | |
3148 | Place a @code{jit-lock-defer-multiline} property on the construct. | |
3149 | This works only if @code{jit-lock-contextually} is used, and with the | |
3150 | same delay before rehighlighting, but like @code{font-lock-multiline}, | |
3151 | it also handles the case where highlighting depends on | |
3152 | subsequent lines. | |
3153 | @end itemize | |
3154 | ||
3155 | @menu | |
3156 | * Font Lock Multiline:: Marking multiline chunks with a text property | |
3157 | * Region to Fontify:: Controlling which region gets refontified | |
3158 | after a buffer change. | |
3159 | @end menu | |
3160 | ||
3161 | @node Font Lock Multiline | |
3162 | @subsubsection Font Lock Multiline | |
3163 | ||
3164 | One way to ensure reliable rehighlighting of multiline Font Lock | |
3165 | constructs is to put on them the text property @code{font-lock-multiline}. | |
3166 | It should be present and non-@code{nil} for text that is part of a | |
3167 | multiline construct. | |
3168 | ||
3169 | When Font Lock is about to highlight a range of text, it first | |
3170 | extends the boundaries of the range as necessary so that they do not | |
3171 | fall within text marked with the @code{font-lock-multiline} property. | |
3172 | Then it removes any @code{font-lock-multiline} properties from the | |
3173 | range, and highlights it. The highlighting specification (mostly | |
3174 | @code{font-lock-keywords}) must reinstall this property each time, | |
3175 | whenever it is appropriate. | |
3176 | ||
3177 | @strong{Warning:} don't use the @code{font-lock-multiline} property | |
3178 | on large ranges of text, because that will make rehighlighting slow. | |
3179 | ||
3180 | @defvar font-lock-multiline | |
3181 | If the @code{font-lock-multiline} variable is set to @code{t}, Font | |
3182 | Lock will try to add the @code{font-lock-multiline} property | |
3183 | automatically on multiline constructs. This is not a universal | |
3184 | solution, however, since it slows down Font Lock somewhat. It can | |
3185 | miss some multiline constructs, or make the property larger or smaller | |
3186 | than necessary. | |
3187 | ||
3188 | For elements whose @var{matcher} is a function, the function should | |
3189 | ensure that submatch 0 covers the whole relevant multiline construct, | |
3190 | even if only a small subpart will be highlighted. It is often just as | |
3191 | easy to add the @code{font-lock-multiline} property by hand. | |
3192 | @end defvar | |
3193 | ||
3194 | The @code{font-lock-multiline} property is meant to ensure proper | |
3195 | refontification; it does not automatically identify new multiline | |
3196 | constructs. Identifying the requires that Font-Lock operate on large | |
3197 | enough chunks at a time. This will happen by accident on many cases, | |
3198 | which may give the impression that multiline constructs magically work. | |
3199 | If you set the @code{font-lock-multiline} variable non-@code{nil}, | |
3200 | this impression will be even stronger, since the highlighting of those | |
3201 | constructs which are found will be properly updated from then on. | |
3202 | But that does not work reliably. | |
3203 | ||
3204 | To find multiline constructs reliably, you must either manually | |
3205 | place the @code{font-lock-multiline} property on the text before | |
3206 | Font-Lock looks at it, or use | |
3207 | @code{font-lock-fontify-region-function}. | |
3208 | ||
3209 | @node Region to Fontify | |
3210 | @subsubsection Region to Fontify after a Buffer Change | |
3211 | ||
3212 | When a buffer is changed, the region that Font Lock refontifies is | |
3213 | by default the smallest sequence of whole lines that spans the change. | |
3214 | While this works well most of the time, sometimes it doesn't---for | |
3215 | example, when a change alters the syntactic meaning of text on an | |
3216 | earlier line. | |
3217 | ||
3218 | You can enlarge (or even reduce) the region to fontify by setting | |
3219 | one the following variables: | |
3220 | ||
3221 | @defvar font-lock-extend-after-change-region-function | |
3222 | This buffer-local variable is either @code{nil} or a function for | |
3223 | Font-Lock to call to determine the region to scan and fontify. | |
3224 | ||
3225 | The function is given three parameters, the standard @var{beg}, | |
3226 | @var{end}, and @var{old-len} from after-change-functions | |
3227 | (@pxref{Change Hooks}). It should return either a cons of the | |
3228 | beginning and end buffer positions (in that order) of the region to | |
3229 | fontify, or @code{nil} (which means choose the region in the standard | |
3230 | way). This function needs to preserve point, the match-data, and the | |
3231 | current restriction. The region it returns may start or end in the | |
3232 | middle of a line. | |
3233 | ||
3234 | Since this function is called after every buffer change, it should be | |
3235 | reasonably fast. | |
3236 | @end defvar | |
3237 | ||
3238 | @node Desktop Save Mode | |
3239 | @section Desktop Save Mode | |
3240 | @cindex desktop save mode | |
3241 | ||
3242 | @dfn{Desktop Save Mode} is a feature to save the state of Emacs from | |
3243 | one session to another. The user-level commands for using Desktop | |
3244 | Save Mode are described in the GNU Emacs Manual (@pxref{Saving Emacs | |
3245 | Sessions,,, emacs, the GNU Emacs Manual}). Modes whose buffers visit | |
3246 | a file, don't have to do anything to use this feature. | |
3247 | ||
3248 | For buffers not visiting a file to have their state saved, the major | |
3249 | mode must bind the buffer local variable @code{desktop-save-buffer} to | |
3250 | a non-@code{nil} value. | |
3251 | ||
3252 | @defvar desktop-save-buffer | |
3253 | If this buffer-local variable is non-@code{nil}, the buffer will have | |
3254 | its state saved in the desktop file at desktop save. If the value is | |
3255 | a function, it is called at desktop save with argument | |
3256 | @var{desktop-dirname}, and its value is saved in the desktop file along | |
3257 | with the state of the buffer for which it was called. When file names | |
3258 | are returned as part of the auxiliary information, they should be | |
3259 | formatted using the call | |
3260 | ||
3261 | @example | |
3262 | (desktop-file-name @var{file-name} @var{desktop-dirname}) | |
3263 | @end example | |
3264 | ||
3265 | @end defvar | |
3266 | ||
3267 | For buffers not visiting a file to be restored, the major mode must | |
3268 | define a function to do the job, and that function must be listed in | |
3269 | the alist @code{desktop-buffer-mode-handlers}. | |
3270 | ||
3271 | @defvar desktop-buffer-mode-handlers | |
3272 | Alist with elements | |
3273 | ||
3274 | @example | |
3275 | (@var{major-mode} . @var{restore-buffer-function}) | |
3276 | @end example | |
3277 | ||
3278 | The function @var{restore-buffer-function} will be called with | |
3279 | argument list | |
3280 | ||
3281 | @example | |
3282 | (@var{buffer-file-name} @var{buffer-name} @var{desktop-buffer-misc}) | |
3283 | @end example | |
3284 | ||
3285 | and it should return the restored buffer. | |
3286 | Here @var{desktop-buffer-misc} is the value returned by the function | |
3287 | optionally bound to @code{desktop-save-buffer}. | |
3288 | @end defvar | |
3289 | ||
3290 | @ignore | |
3291 | arch-tag: 4c7bff41-36e6-4da6-9e7f-9b9289e27c8e | |
3292 | @end ignore |