!A [~LASTIF] $41 |CI0 // If LASTIF is false jump to end of IF command.
#XPUSH 1 !a // Save line number of jump at static nesting level.
#XPUSH 0 !n // Save nesting level in stack 0.
!1 !2 !3 !4 !5 !6 !7 !8 !9
#XPOP 0 Q$ // Restore nesting level into Q.
#XPOP 1 S$ // Restore IF JUMP line number
#XPUSH !q !s // Push it back for the ELSE.
#IF (!n>!q) // after a begin
#FREF END$!r !s // Make IF JUMP goto end of begin block.
#ELSE // same or lower nesting level
#FREF (!a+1) !s // Make IF JUMP goto end of the IF.
#ENDIF