docs: function(newNode, refNode){
        var nodes = this.nodes;
        var pos = refNode ? nodes.indexOf(refNode) : -1;
  
        if (pos == -1)
        {
          nodes.push(newNode);
          this.last = newNode;
        }
        else
          nodes.splice(pos, 0, newNode);
  
        this.first = nodes[0];
  
        newNode.groupNode = this;
  
        this.emit_childNodesModified({ inserted: [newNode] });
      }