[1] As a semantic language, DocBook enables its users to create document content in a presentation-neutral form that captures the logical structure of the content; that content can then be published in a variety of formats, including HTML, XHTML, EPUB, PDF, man pages, WebHelp[2] and HTML Help, without requiring users to make any changes to the source.
In its current version (5.x), DocBook's language is formally defined by a RELAX NG schema with integrated Schematron rules.
(There are also W3C XML Schema+Schematron and Document Type Definition (DTD) versions of the schema available, but these are considered non-standard.)
It is up to an external processing tool or application to decide where on a page the abstract should go and what it should look like or whether or not it should be included in the final output at all.
These elements do not cause the text to break when rendered in a paragraph format, but typically they cause the document processor to apply some kind of distinct typographical treatment to the enclosed text, by changing the font, size, or similar attributes.
XML editing tools can also use schema information to avoid creating non-conforming documents in the first place.
Many graphical or WYSIWYG XML editors come with the ability to edit DocBook like a word processor.
DocBook began in 1991 in discussion groups on Usenet and eventually became a joint project of HAL Computer Systems and O'Reilly & Associates and eventually spawned its own maintenance organization (the Davenport Group) before moving in 1998 to the SGML Open consortium, which subsequently became OASIS.
Starting with DocBook 5, the RELAX NG version is the "normative" form from which the other formats are generated.
Because DocBook was built originally as an application of SGML, the DTD was the only available schema language.
These are XSLT stylesheets that transform DocBook documents into a number of formats (HTML, XSL-FO for later conversion into PDF, etc.).
Users can write their own customized stylesheets or even a full-fledged program to process the DocBook into an appropriate output format as their needs dictate.
Norman Walsh and the DocBook Project development team maintain the key application for producing output from DocBook source documents: A set of XSLT stylesheets (as well as a legacy set of DSSSL stylesheets) that can generate high-quality HTML and print (FO/PDF) output, as well as output in other formats, including RTF, man pages and HTML Help.
Web help[2] is a chunked HTML output format in the DocBook XSL stylesheets that was introduced in version 1.76.1.
Search has stemming, match highlighting, explicit page-scoring, and the standard multilingual tokenizer.
The search and TOC are in a pane that appears as a frameset, but is actually implemented with div tags and cookies (so that it is progressive).
It is a small subset of DocBook designed for single documents such as articles or white papers (i.e., "books" are not supported).
[9] Ingo Schwarze, the author of OpenBSD's mandoc, considers DocBook inferior to the semantic mdoc macro for man pages.
In an attempt to write a DocBook-to-mdoc converter (previous converters like docbook-to-man do not cover semantic elements), he finds the semantic parts "bloated, redundant, and incomplete at the same time" compared to elements covered in mdoc.