Overlays

Overlay controllers coordinate Escape, outside interaction, nested layers, scroll locking, and inert background behavior where applicable.

Topmost rule

Only the topmost overlay should react to Escape or outside dismissal. This prevents parent dialogs or popovers from closing while a child overlay is active.

Modal effects

Dialog modal mode can trap focus, lock scroll, and inert background siblings. These effects are reference-counted so nested dialogs do not unlock the page too early.

Outside interaction

Outside interaction uses the owner document and composed event paths so portals and shadow DOM can be handled by the caller's DOM realm.