OptionalgroupOptionalonOptionalpriorityOptionalwhenOptionalwidget: WidgetOptionalcontextMatcher: ContextMatcherevaluates when clauses with the values that describe the given widget. Defaults
to the ambient context, for toolbars that render items with no owning widget.
Optionalto
evaluates
whenclauses with the values that describe the given widget. Keys scoped to a DOM node keep resolving against the focused element, as no context node is passed here.