It is rather a side effect of the class hierarchy that OnMouseXXX, OnKeyXXX events appears in TMS WEB Core for Visual Studio Code.
The design for TWebPopupMenu is based on its VCL counterpart TPopupMenu that also has no OnMouseXXX, OnKeyXXX events. So, we'd rather look to hide the base class unused events for TWebPopupMenu in TMS WEB Core VSC.
OK, thanks for the explanation.
Addtional issue: When I assign the "OnPopup" event to an event procedure, it compiles, but when running, the browser gives an error message: