How do i control KeyTip 'scoping' inside a Backstage panel?

We don't really have any documentation at the moment for extending to custom controls.  But you can use the KeyTipService.IsKeyTipScope to mark controls that are a scope.  And if an element supports key tips, it can implement IKeyTipTarget and should have the KeyTipService.KeyTipAccessText attached property set.  Sorry but the interface is needed since a method needs to be called on it.  I believe that if you do those things, you can get custom controls working with key tips.

I understand that the interface is needed but i was wondering why instead of the KeyTipService doing a "UIElement as IKeyTipTarget" check only cant it also do a "UIElement.GetValue(KeyTipService.KeyTipTargetProperty) != null" check to figure out if an element supports tips? This way i can attach a KeyTipTarget implementation on my existing controls. Ofc the interface would change slightlly so it gets the actual element as parameter for example 

interface IKeyTipTarget { bool NotifyTipAccessed(UIElement element, string keyTipAccessText); }

At the time all the key tip logic was written (pre-Backstage), there wasn't really a place to inject custom controls into the Ribbon other than the controls we had pre-built, which implemented the interface.  Backstage allows a little more flexibility since you can put custom controls on the tabs.  Note that you don't need to use the interface though.  I believe key tips will still work with a control if it doesn't implement the interface, and it will fall back to focusing the control.