What is XML markup for?
16. The Doctype Declaration
- The DTD is one way of associating the document with its schema (but is not used by W3C or RELAXNG for this purpose)
- The DTD subset is used to provide declarations additional to those in the schema, for example for external files
- The DTD subset may be internal, external, or both
DTDs are now considered old-fashioned — RELAXNG or W3C schemas are preferred.