DanTMan wrote:
O_o It doesn't appear to be used by ParserFunctions, the most widely used one. Or at least I never saw it used till now.
Well, let's look... :D
if ( defined( 'MW_SUPPORTS_PARSERFIRSTCALLINIT' ) ) { $wgHooks['ParserFirstCallInit'][] = array( &$wgExtParserFunctions, 'registerParser' );
That'd done conditionally in a setup function called from $wgExtensionFunctions, in order to provide backwards compatibility with older MediaWiki host versions -- if the ParserFirstCallInit hook isn't available, only then does it go after the parser immediately.
-- brion