It supports only one class per type.
Entries have session scope - a bit untidy.
The Node Type Registry is essentially a 'local' solution , and works well in this situation. It is not ideal, however, when processing XML files about which it has no knowledge. We need a 'standard' way of identifying which classes to use when we encounter a new XML file. Someone 'publishing' an XML document needs a way of telling the world which existing classes are most suitable for this new document. Any entries added to the node type registry remain in memory for the life of the application.