think about.. the various "hierarchies" / aspects / of the relations of the things in it. Event-passing is one ; Containment (x part-of y) is another ; Visual overlap yet another (now that depends on point of view) ; ... there are more.. depending on the purpose.
There're definitely keywords I'm going to Google :) As for hierarchy, I'd like to avoid having class hierarchies where everything is a subclass of Widget, etc. I guess I want to explore how much of the data required for rendering of such UI can lie in contiguous memory — hope it makes sense…
