MShapeWindow [(]SourceShape.w,DestShape.w,X.w,Y.w,Width.w,Height.w[)] ; Cludge Shape within a Shape

Makes a new chunky Shape object based on an existing chunky Shape object,
allowing a `window' within the existing Shape to be used as the new one.
Therefore graphics and cookie data are cludged from the existing Shape's data.
Width should be a multiple of 4 and X,Y specify the top-left corner of the window
within the existing chunky Shape. If used as a function, this command will return
the address of the Shape's graphics data, or 0 for failure.