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(emacs)Font Lock

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Font Lock mode
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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:

   * Invoke `M-x set-face-foreground' or `M-x set-face-background' to
     change the colors of a particular face used by Font Lock.  Note:
     Faces.  The command `M-x list-faces-display' displays all the
     faces currently known to Emacs, including those used by Font Lock.

   * Customize the faces interactively with `M-x customize-face', as
     described in Note: Face Customization.

   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.  (Note: Left Margin Paren.)  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'.