Thank you tomelsten and bermanatalie for your examples.
They were a perfect start for my need: resizing panels using 4 handles.
I got rid of the globals so you can use multiple instances of resizable panels.
Instead, I stored width and height using the text property of 2 hidden shapes inside the right handle (boooh!).
OnLoad, the 4 handles 'jump' automatically to the right place.
So here is the file in case it can be useful.
ResizeByDrag-updated_4handles.rp (103.4 KB)