The XR_MSFT_holographic_window_attachment extension.

This extension enables the runtime to attach to app-provided HolographicSpace and CoreWindow WinRT objects when an XrSession is created. Applications may use this extension to create and control the CoreWindow/App View objects, allowing the app to subscribe to keyboard input events and react to activation event arguments. These events and data would otherwise be inaccessible if the application simply managed the app state and lifetime exclusively through the OpenXR API. This extension is only valid to use where an application can create a CoreWindow, such as UWP applications on the HoloLens.