Function notify_user sends the notification using only the methods that user has enabled from personal notification settings:

www.yoursite.com/notifications/personal

Just like the usual widget process in elgg. Use elgg_register_widget_type() and pass admin as context.

can't do that - entity title is not a metadata..

you need a wheres and an inner join for that, eg.

$db_prefix = elgg_get_config('dbprefix');

'joins' => array("INNER JOIN {$db_prefix}objects_entity o ON (o.guid = e.guid)")

'wheres' => array('o.title = "Rabbit"')

don't forget to use sanitize_string if generating wheres clauses from user data.

It's work with remove the line "group_gatekeeper()" in group page for all plugin, but i think is not a good practice... U know a better method ?