I want to port this Behavior from XamlBehaviorsWpf as a FrameworkElementExtension:

<mtuuc:HeaderedContentControl
    e:FrameworkElementExtensions.CanDragElement="True"
    e:FrameworkElementExtensions.ConstrainDragToParentBounds="True"
    />

The Attached Property option was chosen to not depend on the presence of the Behaviors package. Splitting the CommunityToolkit into smaller libraries is more conducive to using the extension separately if needed.