How to update your plugin to support pop-out windows

Obsidian v0.15 introduced pop-out windows, which each have their own Window, Document, and global constructors. This breaks plugin code that assumes a single global context — for example, appending to document.body or using instanceof checks. The Obsidian API has been updated with new helpers: activeWindow/activeDocument globals, element.win/element.doc accessors, cross-window instanceof via element.instanceOf(), and HTMLElement.onWindowMigrated() for re-initializing complex renderers when an element moves to a different window.