Manual:$wgParserOutputHooks

<translate> This feature was removed completely in version <tvar name=ver>1.41.0</tvar>.</translate>

<translate> Extensions</translate>: $wgParserOutputHooks
Parser output hooks.
<translate> Introduced in version:</translate>	1.11.0
<translate> Deprecated in version:</translate>	1.38.0 (Gerrit change 760994; git #773801e4)
<translate> Removed in version:</translate>	1.41.0 (Gerrit change 942499; git #d421ab57)
<translate> Allowed values:</translate>	(array)
<translate> Default value:</translate>	`[]`
<translate> Other settings:</translate> <translate> Alphabetical</translate> \| <translate> By function</translate>

Details

This is an associative array where the key is an extension-defined tag (typically the extension name), and the value is a PHP callback. These will be called as an OutputPageParserOutput hook, if the relevant tag has been registered with the parser output object.

Registration is done with

$pout->addOutputHook( $tag, $data );

The callback has the form:

function outputHook( $outputPage, $parserOutput, $data ) { 
  /*...*/
}