Coming to Aurora
in 2023 - command bar / ribbon container (see documentation from Radiance
on what you can expect from this container by the time it’s done).
As a sneak peek, here’s the ribbon application menu in action. This menu is a two-pane container where the selection in the first pane displays it’s sub-options in the second pane without opening a cascading secondary popup.
The second pane can display items in different presentation state, has built-in support for vertical scrolling, and can display its own tertiary (and in that case, cascading) popups.