The UI carries out the following steps when drawing a gadget:

•	The draw-interior generic word is called on the value of the interior slot.
•	The draw-gadget* generic word is called on the gadget.
•	The gadget's visible children are drawn, determined by calling visible-children on the gadget.
•	The draw-boundary generic word is called on the value of the boundary slot.

Now, each one of these steps will be covered in detail.
UI pen protocol
Implementing custom drawing logic