code: function isFirstLegendChildOfFieldset(element, parent) {
    return (
      getTag(element) === 'legend' &&
      getTag(parent) === 'fieldset' &&
      element.isSameNode(
        Array.from(parent.children).find(child => getTag(child) === 'legend'),
      )
    )
  }
docs: /*
  According to specification:
  If <fieldset> is disabled, the form controls that are its descendants,
  except descendants of its first optional <legend> element, are disabled
  
  https://html.spec.whatwg.org/multipage/form-elements.html#concept-fieldset-disabled
  
  This method tests whether element is first legend child of fieldset parent