Stepping Outside the Document

The World Inside the Document At present, documents contain all the information used to process them, from XML version numbers to stylesheet identifiers to document type declarations and entities. All references live inside the document, making them hard to modify and maintain.
From Documents to Classes By moving information about document structure, content, and presentation to a central file outside of a document, we can reduce maintenance costs dramatically as well as provide stronger guarantees that documents are what they claim.
Cleaning Up XML By allowing document classes to specify processing, we can remove the issue of 'silent errors' by determining whether or not a processor can live up to its required duties.