docs: function normalize(cells, attr) {
    if(attr) {
      var len = cells.length
      var zipped = new Array(len)
      for(var i=0; i<len; ++i) {
        zipped[i] = [cells[i], attr[i]]
      }
      zipped.sort(compareZipped)
      for(var i=0; i<len; ++i) {
        cells[i] = zipped[i][0]
        attr[i] = zipped[i][1]
      }
      return cells
    } else {
      cells.sort(compareCells)
      return cells
    }
  }