code: function flattenHead(obj) {
      var newHead = [];
  
      _arrayCopy(newHead, obj["head-start"]);
      _arrayCopy(newHead, obj["head"]);
      _arrayCopy(newHead, obj["head-end"]);
  
      delete obj["head-start"];
      delete obj["head-end"];
      obj.head = newHead;
  
      return obj;
  }
docs: Merges `head-start`, `head`, and `head-end` subnodes of the input object into a one `head` subnode and removes the
  other two subnodes.
  @param {Object} obj Object to be manipulated
  @return {Object} the input param object with its `head` node flattened