+ // If this function returns true, keyboard navigation events shouldn't
+ // escape from it. A typical example of such "navigation domain" is a top
+ // level window because pressing TAB in one of them must not transfer focus
+ // to a different top level window. But it's not limited to them, e.g. MDI
+ // children frames are not top level windows (and their IsTopLevel()
+ // returns false) but still are self-contained navigation domains as well.
+ virtual bool IsTopNavigationDomain() const { return false; }
+
+