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23.6.8 Syntactic Font Lock

Syntactic fontification uses a syntax table (see Syntax Tables) to find and highlight syntactically relevant text. If enabled, it runs prior to search-based fontification. The variable font-lock-syntactic-face-function, documented below, determines which syntactic constructs to highlight. There are several variables that affect syntactic fontification; you should set them by means of font-lock-defaults (see Font Lock Basics).

Whenever Font Lock mode performs syntactic fontification on a stretch of text, it first calls the function specified by syntax-propertize-function. Major modes can use this to apply syntax-table text properties to override the buffer's syntax table in special cases. See Syntax Properties.

— Variable: font-lock-keywords-only

If the value of this variable is non-nil, Font Lock does not do syntactic fontification, only search-based fontification based on font-lock-keywords. It is normally set by Font Lock mode based on the keywords-only element in font-lock-defaults.

— Variable: font-lock-syntax-table

This variable holds the syntax table to use for fontification of comments and strings. It is normally set by Font Lock mode based on the syntax-alist element in font-lock-defaults. If this value is nil, syntactic fontification uses the buffer's syntax table (the value returned by the function syntax-table; see Syntax Table Functions).

— Variable: font-lock-beginning-of-syntax-function

If this variable is non-nil, it should be a function to move point back to a position that is syntactically at “top level” and outside of strings or comments. The value is normally set through an other-vars element in font-lock-defaults. If it is nil, Font Lock uses syntax-begin-function to move back outside of any comment, string, or sexp (see Position Parse).

This variable is semi-obsolete; we usually recommend setting syntax-begin-function instead. One of its uses is to tune the behavior of syntactic fontification, e.g., to ensure that different kinds of strings or comments are highlighted differently.

The specified function is called with no arguments. It should leave point at the beginning of any enclosing syntactic block. Typical values are beginning-of-line (used when the start of the line is known to be outside a syntactic block), or beginning-of-defun for programming modes, or backward-paragraph for textual modes.

— Variable: font-lock-syntactic-face-function

If this variable is non-nil, it should be a function to determine which face to use for a given syntactic element (a string or a comment). The value is normally set through an other-vars element in font-lock-defaults.

The function is called with one argument, the parse state at point returned by parse-partial-sexp, and should return a face. The default value returns font-lock-comment-face for comments and font-lock-string-face for strings (see Faces for Font Lock).