ck between them if there's multiple.
      xrButton = new WebXRButton({
        onRequestSession: onRequestSession,
        onEndSession: onEndSession
      });
      document.querySelector('header').appendChild(xrButton.domElement);

      // Is WebXR available on this UA?
      if (navigator.xr) {
        // If the device allows creation of exclusive sessions set it as the
        // target of the 'Enter XR' button.
        navigator.xr.isSessionSupported('immersive-vr').then((supported) => {
          if