Manual:$wgAllowSlowParserFunctions

From Linux Web Expert

<translate> Performance hacks and limits</translate>: $wgAllowSlowParserFunctions
Allow slow parser functions.
<translate> Introduced in version:</translate>1.7.0 (r15276)
<translate> Removed in version:</translate><translate> still in use</translate>
<translate> Allowed values:</translate>(boolean)
<translate> Default value:</translate>false

Details

Enables the magic word {{PAGESINNAMESPACE}}. After that, you can go to Special:Version to check for the existence of the proper parser hook.