Elgg  Version 2.3
documentation/examples/events/trigger.php

Trigger an Elgg Event and attempt to run all handler callbacks registered to that event, type.This function attempts to run all handlers registered to $event, $object_type or the special keyword 'all' for either or both. If a handler returns false, the event will be cancelled (no further handlers will be called, and this function will return false).

$event is usually a verb: create, update, delete, annotation.

$object_type is usually a noun: object, group, user, annotation, relationship, metadata.

$object is usually an Elgg* object associated with the event.

Warning
Elgg events should only be triggered by core. Plugin authors should use trigger_elgg_plugin_hook() instead.

When referring to events, the preferred syntax is "event, type".

Note
Internal: Only rarely should events be changed, added, or removed in core. When making changes to events, be sure to first create a ticket on Github.
Internal: Think of $object_type as the primary namespace element, and $event as the secondary namespace.
Parameters
string$eventThe event type
string$object_typeThe object type
string$objectThe object involved in the event
Returns
bool False if any handler returned false, otherwise true.