# DocBook 4.5

Source: https://xmlvalid.com/schemas/docbook-4.5

> DocBook documents written before version 5: no namespace, DTD instead of RelaxNG.

Many manuals and Linux documentation sets are still DocBook 4.x. Version 4.5 is the last DTD release; DocBook 5 moved to a namespace and RelaxNG.
The DTD is modular; its modules and the ISO entity sets are included here.

- Type: DTD
- Version: 4.5
- Namespace: `No namespace`
- Root element: `book, article, chapter, …`
- Publisher: OASIS DocBook TC (DocBook DTD licence (copy and distribute with the notice)), source: https://docbook.org/xml/4.5/
- Validate against it: https://xmlvalid.com/validate?schema=docbook-4.5

## Notes

- Entities from the DTD ( , © and the other ISO sets) are only known when the DTD is read while parsing, which the browser cannot do for a DOCTYPE that points at docbook.org. Use character references or the five XML entities.
- The example is by xmlvalid.com.