Used in the standard community plugin to gather data for creating activity stream item
More information and full guide can be seen here
Example
class plgCommunityExample extends CApplications { public function onCommunityStreamRender($act) { $actor = CFactory::getUser($act->actor); $stream = new stdClass(); $stream->actor = $actor; $stream->headline = 'Headline'; $stream->message = 'Message'; return $stream; } }