Evaluate an AnchorSource to its current scope: a scope is returned as-is; a tracker's getAnchor() and a getter are read live (so a layer stack's moving top is always current).
getAnchor()
Evaluate an AnchorSource to its current scope: a scope is returned as-is; a tracker's
getAnchor()and a getter are read live (so a layer stack's moving top is always current).