Position:
. should spec out the expectation of how changes to the content effect the Position.

AttributeSet:
. Should spec out which keys resolve up.
. Isn't clear that getAttributeNames doesn't include resolving parent attributes
. What happens when parameter to containsAttribute() are null?

Caret:
. Doesn't spec out what should happen to caret/dot as document changes.
. Should mention that TextUI calls paint on caret.
. Should mention what happens if move dot/caret beyond length of document.