HTML.DefinitionID
TYPE: string/null
DEFAULT: NULL
VERSION: 2.0.0
--DESCRIPTION--

<p>
    Unique identifier for a custom-built HTML definition. If you edit
    the raw version of the HTMLDefinition, introducing changes that the
    configuration object does not reflect, you must specify this variable.
    If you change your custom edits, you should change this directive, or
    clear your cache. Example:
</p>
<pre>
$config = HTMLPurifier_Config::createDefault();
$config->set('HTML', 'DefinitionID', '1');
$def = $config->getHTMLDefinition();
$def->addAttribute('a', 'tabindex', 'Number');
</pre>
<p>
    In the above example, the configuration is still at the defaults, but
    using the advanced API, an extra attribute has been added. The
    configuration object normally has no way of knowing that this change
    has taken place, so it needs an extra directive: %HTML.DefinitionID.
    If someone else attempts to use the default configuration, these two
    pieces of code will not clobber each other in the cache, since one has
    an extra directive attached to it.
</p>
<p>
    You <em>must</em> specify a value to this directive to use the
    advanced API features.
</p>
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