Window, Splitter, ProgressBar Window is the largest gap in the index -- every application needs one and nothing documented it. It states the rules that are not guessable: a window holds exactly one content trinket, its menu bar and status bar are sibling top-level objects rather than children, geometry is in desktop units, and `type` needs a QUOTED string. That last one is worth its own line because every other fixed-vocabulary property in the toolkit takes a bare word: new window type=dialog -> type: expected a quoted string new window type="dialog" -> ok Splitter and ProgressBar are smaller. Both carry a behavior found by running them: a splitter clamps position outside 0.0-1.0 rather than refusing it, and a progress bar re-clamps value when the range changes, so `value=50 minimum=0 maximum=10` still ends at 10 -- the opposite of ListView's selected, where order decides the outcome. Window is added to Home and the sidebar. 48 examples across the seventeen pages run clean against the real registry; 4 are deliberate error demos and 6 are structural skeletons.