Editing DocBook (section)

=== Pre DocBook v5.0 ===

Until DocBook 5, DocBook was defined normatively by a Document Type Definition (DTD). Because DocBook was built originally as an application of [[SGML]], the DTD was the only available schema language. DocBook 4.x formats can be SGML or XML, but the XML version does not have its own namespace.

DocBook 4.x formats had to live within the restrictions of being defined by a DTD. The most significant restriction was that an element name uniquely defines its possible contents. That is, an element named <code>info</code> must contain the same information no matter where it is in the DocBook file. As such, there are many kinds of info elements in DocBook 4.x: <code>bookinfo</code>, <code>chapterinfo</code>, etc. Each has a slightly different content model, but they do share some of their content model. Additionally, they repeat context information. The book's <code>info</code> element is that, because it is a direct child of the book; it does not need to be named specially for a human reader. However, because the format was defined by a DTD, it did have to be named as such. The root element does not have or need a ''version'', as the version is built into the DTD declaration at the top of a pre-DocBook 5 document.

DocBook 4.x documents are not compatible with DocBook 5, but can be converted into DocBook 5 documents via an XSLT stylesheet. One (<code>db4-upgrade.xsl</code>) is provided as part of the distribution of the DocBook 5 schema and specification package.<ref>Jirka Kosek, Norman Walsh, Dick Hamilton, and Michael Smith, ''DocBook V5.0: The Transition Guide'', 16 June 2009, [http://docbook.org/docs/howto/#convert4to5 Converting DocBook V4.x documents to DocBook V5.0]</ref>