[This is preliminary documentation and subject to change.]
For this event, the WinEventProc callback function's hwnd, idObject, and idChild parameters refer to the control with the menu bar or the control activating the context menu.
The hwnd parameter is the handle to the top-level window related to the event. The idObject parameter will be OBJID_MENU or OBJID_SYSMENU for a menu, or OBJID_WINDOW for a pop-up menu. The idChild parameter will be CHILDID_SELF.