register_error($error)
Display an error on next page load.
system_message($message)
Display a system message on next page load.
forward($location="", $reason='system')
Forward to $location.
elgg_echo($message_key, $args=array(), $language="")
Given a message key, returns an appropriately translated full-text string.
elgg_get_logged_in_user_entity()
Return the current logged in user, or null if no user is logged in.
get_user($guid)
Get a user object from a GUID.