Bitrix D7 Events

When to use

• The user needs to control the order in which handlers run for an event — setting the sort/priority argument so one handler runs before or after another.
• The user is declaring a module's event handlers — registering them from the module's include.php/installer, or hooking events of another module such as main:OnBeforeUserAdd or sale:OnSaleOrderSaved.
• The user needs to register an event handler — EventManager::addEventHandler() (D7) or the legacy AddEventHandler() — to react to a module or system event.
• The user is firing a custom event so other code can hook in — constructing an \Bitrix\Main\Event and calling $event->send(), or reading results back from its handlers.