Adds a node using its node name attribute.
CL_DomNode CL_DomNamedNodeMap::set_named_item( const CL_DomNode & node);
Detailed description:
As the node name attribute is used to derive the name which the node must be stored under, multiple nodes of certain types (those that have a "special" string value) cannot be stored as the names would clash. This is seen as preferable to allowing nodes to be aliased.