get _focusableNode() {
      // TODO: [v1]: remove return of _inputNode (it's now here for backwards compatibility)
      // @ts-expect-error see above
      return /** @type {HTMLElement} */ (this._inputNode || document.createElement('input'));
    }
The focusable element:
could be an input, textarea, select, button or any other element with tabindex > -1
@protected
@type {HTMLElement}