Drop coordinates for mouseDrop

I am trying to handle a mouseDrop on a diagram. need to know if the drop is to the left of the drop target center or to the right. I have what I believe is the drop target center… and please tell me if I am wrong… via graphObject.part.location where graphObject is the 2nd argument to the mouseDrop handler. Now, how do I get the precise location of the drop?
I have tried inputEvent.getCurrentPosition(), but I get …is not a function.

thanks for your help.

inputEvent.documentPoint, for document coordinates (coordinates in the Diagram document)

inputEvent.viewPoint, for view coordinates (coordinates in the Div itself)