the layer, layerItem and layerNode

I am very confuse the relationship among the layer, layerItem and layerNode, and how they work?
Who can explain it for me, i will very appreciate!

Well, without deep look into you don't need more than knowledge about layers. http://www.ogre3d.org/wiki/index.php/MyGUI_layers
LayedNode is singe piece of geometry. In terms ow widgets LayedNode is root widgets with all attached child widgets and hierarchy.
LayerItem is item in hierarchy. Every widget is LayerItem.

Why do you need to know that?

Altren
thanks for your reply , because i want to study MyGui deeply, so i am reading the source code and feel confuse about thesethings.