which grob?

[ji3m]

In the following program

export spin ()
begin
Rect_P (); <--- who does this clear.?
CHOOSE (...); <--- where does this draw
TEXTOUT_P("hello",0,0); <-- where does this draw
while 1 do end;
end;

What grob am i writing to.?

if i break out i return to the starting screen.
The choose box opens on top of the starting screen which is untouched.

What exactly is the graphics paradigm here?