There are several variables that control how Font Lock mode highlights
text. But major modes should not set any of these variables directly.
Instead, they should set
font-lock-defaults as a buffer-local
variable. The value assigned to this variable is used, if and when Font
Lock mode is enabled, to set all the other variables.
This variable is set by major modes to specify how to fontify text in
that mode. It automatically becomes buffer-local when set. If its
nil, Font Lock mode does no highlighting, and you can
use the ‘Faces’ menu (under ‘Edit’ and then ‘Text
Properties’ in the menu bar) to assign faces explicitly to text in the
nil, the value should look like this:
(keywords [keywords-only [case-fold [syntax-alist [syntax-begin other-vars…]]]])
The first element, keywords, indirectly specifies the value of
font-lock-keywords which directs search-based fontification.
It can be a symbol, a variable or a function whose value is the list
to use for
font-lock-keywords. It can also be a list of
several such symbols, one for each possible level of fontification.
The first symbol specifies the ‘mode default’ level of
fontification, the next symbol level 1 fontification, the next level 2,
and so on. The ‘mode default’ level is normally the same as level
1. It is used when
font-lock-maximum-decoration has a
value. See Levels of Font Lock.
The second element, keywords-only, specifies the value of the
font-lock-keywords-only. If this is omitted or
nil, syntactic fontification (of strings and comments) is also
performed. If this is non-
nil, syntactic fontification is not
performed. See Syntactic Font Lock.
The third element, case-fold, specifies the value of
font-lock-keywords-case-fold-search. If it is non-
Font Lock mode ignores case during search-based fontification.
If the fourth element, syntax-alist, is non-
nil, it should
be a list of cons cells of the form
. string). These are used to set up a syntax table for syntactic
fontification; the resulting syntax table is stored in
font-lock-syntax-table. If syntax-alist is omitted or
nil, syntactic fontification uses the syntax table returned by
syntax-table function. See Syntax Table Functions.
The fifth element, syntax-begin, specifies the value of
font-lock-beginning-of-syntax-function. We recommend setting
this variable to
nil and using
All the remaining elements (if any) are collectively called
other-vars. Each of these elements should have the form
(variable . value)—which means, make
variable buffer-local and then set it to value. You can
use these other-vars to set other variables that affect
fontification, aside from those you can control with the first five
elements. See Other Font Lock Variables.
If your mode fontifies text explicitly by adding
font-lock-face properties, it can specify
(nil t) for
font-lock-defaults to turn off all automatic fontification.
However, this is not required; it is possible to fontify some things
font-lock-face properties and set up automatic
fontification for other parts of the text.