function querySelectorExt(eltOrSelector, selector) {
    if (typeof eltOrSelector !== 'string') {
      return querySelectorAllExt(eltOrSelector, selector)[0]
    } else {
      return querySelectorAllExt(getDocument().body, eltOrSelector)[0]
    }
  }
@param {Node|string} eltOrSelector
@param {string=} selector
@returns {Node|Window}