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35.4 Syntax Properties

When the syntax table is not flexible enough to specify the syntax of a language, you can override the syntax table for specific character occurrences in the buffer, by applying a syntax-table text property. See Text Properties, for how to apply text properties.

The valid values of syntax-table text property are:


If the property value is a syntax table, that table is used instead of the current buffer’s syntax table to determine the syntax for the underlying text character.

(syntax-code . matching-char)

A cons cell of this format is a raw syntax descriptor (see Syntax Table Internals), which directly specifies a syntax class for the underlying text character.


If the property is nil, the character’s syntax is determined from the current syntax table in the usual way.

variable parse-sexp-lookup-properties

If this is non-nil, the syntax scanning functions, like forward-sexp, pay attention to syntax-table text properties. Otherwise they use only the current syntax table.

variable syntax-propertize-function

This variable, if non-nil, should store a function for applying syntax-table properties to a specified stretch of text. It is intended to be used by major modes to install a function which applies syntax-table properties in some mode-appropriate way.

The function is called by syntax-ppss (see Position Parse), and by Font Lock mode during syntactic fontification (see Syntactic Font Lock). It is called with two arguments, start and end, which are the starting and ending positions of the text on which it should act. It is allowed to call syntax-ppss on any position before end, but if a Lisp program calls syntax-ppss on some position and later modifies the buffer at some earlier position, then it is that program’s responsibility to call syntax-ppss-flush-cache to flush the now obsolete info from the cache.

Caution: When this variable is non-nil, Emacs removes syntax-table text properties arbitrarily and relies on syntax-propertize-function to reapply them. Thus if this facility is used at all, the function must apply all syntax-table text properties used by the major mode. In particular, Modes derived from a CC Mode mode must not use this variable, since CC Mode uses other means to apply and remove these text properties.

variable syntax-propertize-extend-region-functions

This abnormal hook is run by the syntax parsing code prior to calling syntax-propertize-function. Its role is to help locate safe starting and ending buffer positions for passing to syntax-propertize-function. For example, a major mode can add a function to this hook to identify multi-line syntactic constructs, and ensure that the boundaries do not fall in the middle of one.

Each function in this hook should accept two arguments, start and end. It should return either a cons cell of two adjusted buffer positions, (new-start . new-end), or nil if no adjustment is necessary. The hook functions are run in turn, repeatedly, until they all return nil.