Signalled by cache versions of parser wrapper functions inc/parserutils.php. Syntax plugins can use this event to provide their own assistance to DokuWiki's cache validity logic when the syntax extension adds other dependencies to the rendered page.
$data is a cache object – refer inc/cache.php.
For handling the event, key properties of the cache object are:
The following plugins are known to handle this event and their source code may be a good start for understanding and implementing a handler yourself.