Floating panel groups dropped on another group's top or bottom edge join it
in a set: the groups stack top to bottom, move together by the top group's
title bar (whose × docks them all), and a group dragged by its tab strip
leaves the set. A double-click on a tab collapses a group to its tabs.
Sets and collapsed groups are kept in preferences and workspaces, and
window.panel.float takes below, above and collapsed.
Behaviour from public documentation:
https://helpx.adobe.com/illustrator/using/workspace-basics.html
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CC5DiGJEZ5ADaQMBEQk4W1
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