An event handler defines the work to be performed upon the firing of a particular event. Each event handler is uniquely identified in the system with the combination of an event name and a handler sequence number.
Each event can have multiple event handlers that execute when the event fires. In such cases, the handler sequence number and other factors determine the order in which event handlers are actually processed.
An event handler can be restricted to execute only in relation to a specific set of conditions. For example, a particular event handler might be defined to execute only when the associated event is triggered by an action on a particular form or when a particular IDO is involved.
For more information on these and other event handler settings, see "About the Application Event System" in the Guide to the Application Event System.