standard SGML representation system for technical documents DocBook is an SGML document type definition (DTD) that is well-suited to books, articles, or reference documentation about technical matters, systems, or software (although it is by no means limited to these applications). It has emerged as an open and standard DTD in the software industry, and is used as the documentation system of choice for many free software projects. This package contains the SGML DTD for DocBook, which describes the formal structure for documents following this format. If you wish to author DocBook documents using XML rather than SGML, use the 'docbook-xml' package. You will need other packages in order to edit (psgml), validate (opensp) or format (docbook-xsl, docbook-dsssl) DocBook documents. This package includes the 2.4.1, 3.0, 3.1, 4.0, 4.1, 4.2 and 4.3 versions of the DocBook SGML DTD.