OptionalattachRegion trackers (e.g. FocusActivation) implement this: start watching rootElement as the
region of interest, returning the detach. A CommandAnchorProvider in 'synthetic'
key-delivery mode bounds its tracker to the seam element through this — the anchor follows
focus within exactly the subtree whose unconsumed keys the seam delivers. Absent on
code-driven trackers (ManualActivation).
The current anchor scope, or null before any activation.
OptionalgetThe DOM region this tracker watches, if any (e.g. a FocusActivation's attached root), or
null/absent for code-driven trackers (ManualActivation). A CommandResolver
uses it to attach keystroke handling on the same element the anchor follows — keybinds
in lockstep with focus, no separate provider. subscribe fires when this changes.
Fires when the anchor changes — and, for region trackers, when the region attaches/detaches.
Produces "the current anchor" (resolution leaf) for a CommandResolver and notifies when it changes. The activation strategy, pluggable per container: focus-driven (
FocusActivation, region-scoped) or code-driven (ManualActivation).