23.5.5 Faces for Font Lock

You can make Font Lock mode use any face, but several faces are defined specifically for Font Lock mode. Each of these symbols is both a face name, and a variable whose default value is the symbol itself. Thus, the default value of font-lock-comment-face is font-lock-comment-face. This means you can write font-lock-comment-face in a context such as font-lock-keywords where a face-name-valued expression is used.

font-lock-comment-face

Used (typically) for comments.

font-lock-string-face

Used (typically) for string constants.

font-lock-keyword-face

Used (typically) for keywords--names that have special syntactic significance, like for and if in C.

font-lock-builtin-face

Used (typically) for built-in function names.

font-lock-function-name-face

Used (typically) for the name of a function being defined or declared, in a function definition or declaration.

font-lock-variable-name-face

Used (typically) for the name of a variable being defined or declared, in a variable definition or declaration.

font-lock-type-face

Used (typically) for names of user-defined data types, where they are defined and where they are used.

font-lock-constant-face

Used (typically) for constant names.

font-lock-warning-face

Used (typically) for constructs that are peculiar, or that greatly change the meaning of other text. For example, this is used for `;;;###autoload' cookies in Emacs Lisp, and for #error directives in C.