docs: function fullscreenchangeHandler() {
          viewerAPI.fire('fullscreenchange');
          if (isFullscreen()) {
              $el.addClass('crocodoc-fullscreen');
              viewerAPI.fire('fullscreenenter');
          } else {
              $el.removeClass('crocodoc-fullscreen');
              viewerAPI.fire('fullscreenexit');
          }
      }