The DocBook DTD defines structural and content-based SGML and XML markup for computer documentation, with a primary emphasis on software documentation and related classes of technical documents. Its main high-level hierarchical structures are for books, reference entries (for example, ``man pages''), and articles. It is maintained by the DocBook Technical Committee of OASIS (the Organization for the Advancement of Structured Information Standards), www.oasis-open.org. Documentation on DocBook is available at http://docbook.org This package contains DocBook SGML versions 2.4.1, 3.0, 3.1, 4.0, 4.1, and 4.2. XML versions are in the docbook-xml package.