docs: function levelSorter(a, b) {
    var l = Math.max(a.length, b.length)
    for (var i = 0; i < l; i += 1) {
      if (!(i in a)) return +1
      if (!(i in b)) return -1
  
      if (a.length < b.length) return +1
      if (a.length > b.length) return -1
    }
  }