This is a tool for Morph development and improving the performance of morphs. It lets you see how much drawing is being done but clipped (overdraw). If your morph is drawing excessive clipped stuff, you may want to fix this to improve performance.
Adds a Preference called 'debugShowOverdraw' under 'debug' to allow TransformMorph clipping to be disabled. All drawing done by morphs in the TransformMorph, normally clipped away, will be visible.