ActiveX Controls have been deprecated by Microsoft in the latest versions of the Windows operating system in favor of the DotNet framework and its controls.
While MAXScript still supports ActiveX controls, these have to be installed and registered on the system to be accessible to MAXScript.
As a replacement of ActiveX controls, MAXScript supports DotNet controls in 3ds Max 9 and higher.
Events are notifications sent by the ActiveX controls to the rollout, whenever an action is performed on the control, e.g.: clicking a button, browsing to a webpage. If supporting event handler is implemented for the event, in the rollout context, the handler is called with supporting arguments.
For a list of all available events, you can use the ActiveX Control Inspector Function
showEvents <axControl>