Backstage, Top Bar, and QAT

The ribbon exposes several high-value content slots in addition to tabs and groups:

Ribbon.TopBarStartContent
Ribbon.TopBarCenterContent
Ribbon.TopBarEndContent
Ribbon.HeaderStartContent
Ribbon.HeaderEndContent
Ribbon.Backstage

The quick access toolbar is driven by:

QuickAccessItems
QuickAccessPlacement
RibbonQuickAccessPlacement

The sample applications show the intended combinations:

XAML-only sample: static backstage shell and static top-bar/header content.
MVVM-only sample: dynamic command catalog, quick access items, and state ownership toggles.
Hybrid sample: static XAML shell with dynamic ribbon tab contributions.