code: function _LightDismissableLayer_shown(client /*: ILightDismissable */) {
                      client._focusable = true;
                      var index = this._clients.indexOf(client);
                      if (index === -1) {
                          this._clients.push(client);
                          client.onShow(this);
                          if (!_LightDismissService.isShown(this)) {
                              _LightDismissService.shown(this);
                          } else {
                              _LightDismissService.updated(this);
                              this._activateTopFocusableClientIfNeeded();
                          }
                      }
                  }
docs: Dismissables should call this as soon as they are ready to be shown. More specifically, they should call this: - After they are in the DOM and ready to receive focus (e.g. style.display cannot be "none") - Before their entrance animation is played