First outer loop index. When loops are nested, this pushes the value of the first (or only) outer loop onto the stack.

# Show the trace log, clear it, then show the order of I (inner loop) and J (outer loop).
ShowTraceLog 
ClearTraceLog 
3 1 do 
	12 10 do 
		I J Trace2
	loop 
loop

#10 1
#11 1
#10 2
#11 2