GOP-dissected.txt

A patch with sub-patch. The sub-patch has a GOP. The size of the sub-patch and its position on the screen is in its declaration:
#N canvas 228 231 450 300 subPatch 1;
           |   |   |   |
      screen pos    size

The size and position of the GOP on the sub-patch is in the coords line:
#X coords 0 -1 1 1 200 200 1 0 0;
                    |   |    | |
                     size    pos

The position of the GOP on the parent is in the restore line:
#X restore 1 18 pd subPatch;
           |  |
            pos (top-left conner)



#N canvas 604 239 450 300 10;
#N canvas 228 231 450 300 subPatch 1;
#X obj 2 2 iemguts/receivecanvas 1;
#X obj 251 16 inlet;
#X obj 8 224 outlet;
#X obj 190 229 outlet;
#X obj 87 109 bng 15 250 50 0 empty empty empty 17 7 0 10 -262144 -1
-1;
#X connect 0 0 2 0;
#X connect 0 0 4 0;
#X connect 0 1 3 0;
#X connect 1 0 0 0;
#X coords 0 -1 1 1 200 200 1 0 0;
#X restore 1 18 pd subPatch;
#X obj 103 252 print;
#X msg 337 38 status;
#X connect 0 0 1 0;
#X connect 2 0 0 0;



mouseCanvas (as derived from receivecanvas) uses a proxy object to collect mouse events from its own or higher canvasses. canvasposition retrieves the GOP position on its parent or higher canvas. 
Confusing is that canvasposition 0 reports the position of the GOP on the parent canvas.