The draw order is determined by which registerDraw() is called first. Typically the registerDraw is set in the setup of the class, or when the object is created. So if you have two objects that have the registerDraw in them, the one created first will be drawn before (under) the others. 

Sometimes it is necessary to set up an object first but also have it drawn on top. In this case I would create a beginDraw() method on my class that would call the registerDraw method. then you can create them in any order and set up their draw order later on (or even change the order by using unregisterDraw).

For the easiest control of draw order, I like to just include a draw() method in my classes and call them explicitly. you can also nest the drawing, so you call draw to your container class then it calls draw to all it's objects.

I hope that makes sense,

Good Luck,

ak