An overlay could be modal - the document underneath shut out entirely - or
passive, which a tooltip wants: painted above, taking no input at all. What
neither of those is is a control that floats over a scroll and can still be
clicked, which is why the file tree's reveal button had to sit above or below
its scroll and shove the rows about when it appeared.

Overlay takes an OverlayMode of three now. A floating one is painted above
everything and is interacted before the rest, and only the part of the
document it actually covers is shut out for that frame, so a press that lands
on it does not also land on the row underneath and everything around it stays
live. Its content joins the tab order, since it is something a reader can
reach.

unstyled::Floating is the component: it pins its child to the top or the
bottom edge of a node named by a NodeRef, through two placements - InsideTop
and InsideBottom - that put content inside the anchor rather than beside it.
It takes no space in the layout around it, which is the whole point.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MBQJGiJxUECw86CYG9JZNk