if the mouse is over a selected region, or no region, this method returns all selected regions.
if the mouse is over an unselected region, just that region is returned.
-For other edit points the method returns the selected regions AND those that are both under the edit position
-AND on a selected track, or on a track which is in the same active edit-enabled route group as a selected
-region.
+For other edit points the method returns the selected regions. If no regions are selected, it returns
+the regions under the edit position on the selected tracks.
The action handlers call the appropriate method to decide which regions to operate on.