As the user moves the cursor into, over and out of a Control that has been designated
as a DropTarget, events indicate what operation can be performed and what data can be
transferred if a drop where to occur at that point.
The application can respond to these events and change the type of data that will
be dropped by modifying event.currentDataType, or change the operation that will be performed
by modifying the event.detail field or stop any drop from happening on the current target
by setting the event.detail field to DND_DROP_NONE.
When the user causes a drop to happen by releasing the mouse over a valid drop target,
the application has one last chance to change the data type of the drop through the
DropAccept event. If the drop is still allowed, the DropAccept event is immediately
followed by the Drop event. In the Drop event, the application can still change the
operation that is performed but the data type is fixed.