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 But this usage is obsolete.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