To manually turn FontLockMode on or off use either the Options → Syntax Highlighting in the menu, or type ‘M-x font-lock-mode’. Both toggle the option when you use them.

To turn on font-lock automatically every time you start Emacs either edit your InitFile (shown below) or turn it on via the menu with Options → Save Options.

Here’s what you can put in your InitFile to enable font-lock globally. It works for both Emacs and XEmacs.

(if (fboundp 'global-font-lock-mode)
    (global-font-lock-mode 1)        ; GNU Emacs
  (setq font-lock-auto-fontify t))   ; XEmacs

As to adding your own keywords, see AddKeywords.

In SXEmacs, I’ve found that I need to add the following to my ~/.sxemacs/init.el file in order for newly visited files to have font-lock-mode turned on:

(setq font-lock-auto-fontify t)
(add-hook 'find-file-hooks (lambda () (font-lock-mode 1)))


Which files are then highlighted?

In an Emacs 21.4.1 with global-font-lock-mode on, it works with LISP, C, HTML, … but not for instance with .css oder .js. Is it because of the Emacs version?

For syntax highlighting to work there must be a major mode for it. There are major modes for both .css (CssMode) and .js (JavaScriptMode)

Also check the ‘font-lock-maximum-size’ variable

CategoryFaces ComparativeEmacsology