code: function(zIndex) {
              if (!this.parent) {
                  Kinetic.Util.warn('Node has no parent. zIndex parameter is ignored.');
                  return;
              }
              var index = this.index;
              this.parent.children.splice(index, 1);
              this.parent.children.splice(zIndex, 0, this);
              this.parent._setChildrenIndices();
              return this;
          }
docs: set zIndex relative to siblings
  @method
  @memberof Kinetic.Node.prototype
  @param {Integer} zIndex
  @returns {Kinetic.Node}