code: function isHeadingRow (tr) {
    var parentNode = tr.parentNode
    return (
      parentNode.nodeName === 'THEAD' ||
      (
        parentNode.firstChild === tr &&
        (parentNode.nodeName === 'TABLE' || isFirstTbody(parentNode)) &&
        every.call(tr.childNodes, function (n) { return n.nodeName === 'TH' })
      )
    )
  }
docs: A tr is a heading row if: - the parent is a THEAD - or if its the first child of the TABLE or the first TBODY (possibly following a blank THEAD) - and every cell is a TH