emacs: Font Lock
14.12 Font Lock mode
====================
Font Lock mode is a minor mode, always local to a particular buffer,
which assigns faces to (or “fontifies”) the text in the buffer. Each
buffer’s major mode tells Font Lock mode which text to fontify; for
instance, programming language modes fontify syntactically relevant
constructs like comments, strings, and function names.
Font Lock mode is enabled by default. To toggle it in the current
buffer, type ‘M-x font-lock-mode’. A positive numeric argument
unconditionally enables Font Lock mode, and a negative or zero argument
disables it.
Type ‘M-x global-font-lock-mode’ to toggle Font Lock mode in all
buffers. To impose this setting for future Emacs sessions, customize
the variable ‘global-font-lock-mode’ (
Easy Customization), or
add the following line to your init file:
(global-font-lock-mode 0)
If you have disabled Global Font Lock mode, you can still enable Font
Lock for specific major modes by adding the function ‘font-lock-mode’ to
the mode hooks (Hooks). For example, to enable Font Lock mode
for editing C files, you can do this:
(add-hook 'c-mode-hook 'font-lock-mode)
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 ‘M-x customize-group <RET>
font-lock-faces <RET>’. You can then use that customization buffer to
customize the appearance of these faces. Face Customization.
You can customize the variable ‘font-lock-maximum-decoration’ to
alter the amount of fontification applied by Font Lock mode, for major
modes that support this feature. The value should be a number (with 1
representing a minimal amount of fontification; some modes support
levels as high as 3); or ‘t’, meaning “as high as possible” (the
default). To be effective for a given file buffer, the customization of
‘font-lock-maximum-decoration’ should be done _before_ the file is
visited; if you already have the file visited in a buffer when you
customize this variable, kill the buffer and visit the file again after
the customization.
You can also specify different numbers for particular major modes;
for example, to use level 1 for C/C++ modes, and the default level
otherwise, use the value
'((c-mode . 1) (c++-mode . 1)))
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 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. Therefore, you should avoid placing an
open-parenthesis or open-brace in the leftmost column, if it is inside a
string or comment. Left Margin Paren, for details.
Font Lock highlighting patterns already exist for most 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:
(add-hook 'c-mode-hook
(lambda ()
(font-lock-add-keywords nil
'(("\\<\\(FIXME\\):" 1
font-lock-warning-face t)))))
To remove keywords from the font-lock highlighting patterns, use the
function ‘font-lock-remove-keywords’. (elisp)Search-based
Fontification.
Fontifying large buffers can take a long time. To avoid large delays
when a file is visited, Emacs initially fontifies only the visible
portion of a buffer. As you scroll through the buffer, each portion
that becomes visible is fontified as soon as it is displayed; this type
of Font Lock is called “Just-In-Time” (or “JIT”) Lock. You can control
how JIT Lock behaves, including telling it to perform fontification
while idle, by customizing variables in the customization group
‘jit-lock’. Specific Customization.
Info Catalog
emacs: Text Scale
emacs: Display
emacs: Highlight Interactively