Manual talk:Hooks/LinkerMakeExternalLink

This example is incorrect. The call in Linker.php is:

$success = wfRunHooks('LinkerMakeExternalLink', array( &$url, &$text, &$link ) );

That is, the code needs to be updated to pass the attributes variable or the example needs amending to remove the $attribs parameter.
 * This is correct, $attribs has been added in 1.15. i Alex  11:36, 20 March 2009 (UTC)