Not recognized VRML/X3D node type. Used for nodes found when parsing VRML/X3D file that are not implemented.
TX3DUnknownNode is parsed (in classic VRML encoding) in a special way, to be able to omit it gracefully. While such "unknown" node doesn't really do match in our graph, it works correctly with VRML/X3D DEF/USE mechanism.
Never instantiate this class by a standard constructor. Always use CreateUnknown constructor, this way we can safely assume that NodeTypeName is always correctly set.