path: root/devdocs/elisp/syntax-properties.html

 <h3 class="section">Syntax Properties</h3>  <p>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 <code>syntax-table</code> text property. See <a href="text-properties">Text Properties</a>, for how to apply text properties. </p> <p>The valid values of <code>syntax-table</code> text property are: </p> <dl compact> <dt><var>syntax-table</var></dt> <dd>
<p>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. </p> </dd> <dt><code>(<var>syntax-code</var> . <var>matching-char</var>)</code></dt> <dd>
<p>A cons cell of this format is a raw syntax descriptor (see <a href="syntax-table-internals">Syntax Table Internals</a>), which directly specifies a syntax class for the underlying text character. </p> </dd> <dt><code>nil</code></dt> <dd><p>If the property is <code>nil</code>, the character’s syntax is determined from the current syntax table in the usual way. </p></dd> </dl> <dl> <dt id="parse-sexp-lookup-properties">Variable: <strong>parse-sexp-lookup-properties</strong>
</dt> <dd><p>If this is non-<code>nil</code>, the syntax scanning functions, like <code>forward-sexp</code>, pay attention to <code>syntax-table</code> text properties. Otherwise they use only the current syntax table. </p></dd>
</dl> <dl> <dt id="syntax-propertize-function">Variable: <strong>syntax-propertize-function</strong>
</dt> <dd>
<p>This variable, if non-<code>nil</code>, should store a function for applying <code>syntax-table</code> properties to a specified stretch of text. It is intended to be used by major modes to install a function which applies <code>syntax-table</code> properties in some mode-appropriate way. </p> <p>The function is called by <code>syntax-ppss</code> (see <a href="position-parse">Position Parse</a>), and by Font Lock mode during syntactic fontification (see <a href="syntactic-font-lock">Syntactic Font Lock</a>). It is called with two arguments, <var>start</var> and <var>end</var>, which are the starting and ending positions of the text on which it should act. It is allowed to arbitrarily move point within the region delimited by <var>start</var> and <var>end</var>; such motions don’t need to use <code>save-excursion</code> (see <a href="excursions">Excursions</a>). It is also allowed to call <code>syntax-ppss</code> on any position before <var>end</var>, but if a Lisp program calls <code>syntax-ppss</code> on some position and later modifies the buffer at some earlier position, then it is that program’s responsibility to call <code>syntax-ppss-flush-cache</code> to flush the now obsolete info from the cache. </p> <p><strong>Caution:</strong> When this variable is non-<code>nil</code>, Emacs removes <code>syntax-table</code> text properties arbitrarily and relies on <code>syntax-propertize-function</code> to reapply them. Thus if this facility is used at all, the function must apply <strong>all</strong> <code>syntax-table</code> 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. </p>
</dd>
</dl> <dl> <dt id="syntax-propertize-extend-region-functions">Variable: <strong>syntax-propertize-extend-region-functions</strong>
</dt> <dd>
<p>This abnormal hook is run by the syntax parsing code prior to calling <code>syntax-propertize-function</code>. Its role is to help locate safe starting and ending buffer positions for passing to <code>syntax-propertize-function</code>. 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. </p> <p>Each function in this hook should accept two arguments, <var>start</var> and <var>end</var>. It should return either a cons cell of two adjusted buffer positions, <code>(<var>new-start</var> . <var>new-end</var>)</code>, or <code>nil</code> if no adjustment is necessary. The hook functions are run in turn, repeatedly, until they all return <code>nil</code>. </p>
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