I don't mean doing it in a retained-mode-like way with a data structure in memory, I mean special casing certain UI elements. For example, a blinking cursor could be a special path through the code which updates only the pixels where the blinking cursor is, while the rest of the window just reuses the last drawn frame (kinda like how mouse cursors are handled in hardware). Similar tricks work for things like hover highlights and context menus.

No need for a retained data structure to implement the above.