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Font Lock mode is a minor mode, always local to a particular buffer, which highlights (or "fontifies") using various faces according to the syntax of the text you are editing. It can recognize comments and strings in most languages; in several languages, it can also recognize and properly highlight various other important constructs--for example, names of functions being defined or reserved keywords.
The command M-x font-lock-mode turns Font Lock mode on or off
according to the argument, and toggles the mode when it has no argument.
The function turn-on-font-lock unconditionally enables Font Lock
mode. This is useful in mode-hook functions. For example, to enable
Font Lock mode whenever you edit a C file, you can do this:
(add-hook 'c-mode-hook 'turn-on-font-lock) |
To turn on Font Lock mode automatically in all modes which support
it, customize the user option global-font-lock-mode or use the
function global-font-lock-mode in your `.emacs' file, like
this:
(global-font-lock-mode 1) |
Font Lock mode uses several specifically named faces to do its job,
including font-lock-string-face, font-lock-comment-face,
and others. The easiest way to find them all is to use completion
on the face name in set-face-foreground.
To change the colors or the fonts used by Font Lock mode to fontify different parts of text, just change these faces. There are two ways to do it:
To get the full benefit of Font Lock mode, you need to choose a default font which has bold, italic, and bold-italic variants; or else you need to have a color or gray-scale screen.
The variable font-lock-maximum-decoration specifies the
preferred level of fontification, for modes that provide multiple
levels. Level 1 is the least amount of fontification; some modes
support levels as high as 3. The normal default is "as high as
possible." You can specify an integer, which applies to all modes, or
you can specify different numbers for particular major modes; for
example, to use level 1 for C/C++ modes, and the default level
otherwise, use this:
(setq font-lock-maximum-decoration
'((c-mode . 1) (c++-mode . 1)))
|
Fontification can be too slow for large buffers, so you can suppress
it. The variable font-lock-maximum-size specifies a buffer size,
beyond which buffer fontification is suppressed.
Comment and string fontification (or "syntactic" fontification) relies on analysis of the syntactic structure of the buffer text. For the sake of speed, some modes, including C mode and Lisp mode, rely on a special convention: an open-parenthesis or open-brace in the leftmost column always defines the beginning of a defun, and is thus always outside any string or comment. (See section U.2.1 Left Margin Convention.) If you don't follow this convention, Font Lock mode can misfontify the text that follows an open-parenthesis or open-brace in the leftmost column that is inside a string or comment.
The variable font-lock-beginning-of-syntax-function (always
buffer-local) specifies how Font Lock mode can find a position
guaranteed to be outside any comment or string. In modes which use the
leftmost column parenthesis convention, the default value of the variable
is beginning-of-defun---that tells Font Lock mode to use the
convention. If you set this variable to nil, Font Lock no longer
relies on the convention. This avoids incorrect results, but the price
is that, in some cases, fontification for a changed text must rescan
buffer text from the beginning of the buffer. This can considerably
slow down redisplay while scrolling, particularly if you are close to
the end of a large buffer.
Font Lock highlighting patterns already exist for many modes, but you
may want to fontify additional patterns. You can use the function
font-lock-add-keywords, to add your own highlighting patterns for
a particular mode. For example, to highlight `FIXME:' words in C
comments, use this:
(font-lock-add-keywords
'c-mode
'(("\\<\\(FIXME\\):" 1 font-lock-warning-face t)))
|
To remove keywords from the font-lock highlighting patterns, use the
function font-lock-remove-keywords.
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