Unlike ABL widget events, ActiveX control events often pass parameters. Also, while there are a few standard events common to most ActiveX controls, there are an infinite variety of possible events that are unique to each ActiveX control. Because ABL cannot have direct knowledge of all these possible events and must be able to handle the parameters of many of them, the standard ABL trigger mechanism cannot handle them.

Instead, ABL allows you to handle ActiveX control events using OCX event procedures. An OCX event procedure is a standard ABL internal procedure that serves as an event handler for ActiveX controls. The parameter-passing mechanism provided for ABL procedures handles most parameters that ActiveX control events typically pass. ABL identifies an OCX event procedure from the way its name is put together. This is the only syntactic feature that distinguishes the ABL internal procedure as an OCX event procedure.