The TEI Guidelines, its DTD, and its schema fragments, are all produced from a single XML resource containing:

1. Descriptive prose (lots of it)
2. Examples of usage (plenty)
3. Formal declarations for components of the TEI Abstract Model:
   • elements and attributes
   • modules
   • classes and macros
4. We call this resource an ODD (One Document Does it all) although the master source is instantiated as a gazillion XML mini-documents.