Robust open source application of XML for technical documentation (but also for general documentation) with a large worldwide base of users
Non-structured Documentation
It is based on the WYSIWYG ("What You See Is What You Get") mindset.
The semantic structure of documents is largely or totally ignored.
You concentrate on the physical layout of documents, whether on screen or in print.
You typically use a word processor such as OpenOffice.org Writer and Word without "styles".
Structured Documentation in XML
It is based on the WYSIWYM ("What You See Is What You Mean") philosophy.
The physical layout of documents is separated from the content.
You concentrate on and tag the semantic structure of documents.
You typically use a text/XML editor.
Advantages of XML
"Write Once, Publish Anywhere" - You have only to prepare single documents; you can either use them as they are with stylesheets or convert them later to different physical media and formats including plain text, HTML/XHTML, RTF, PDF and TeX.
Since your documents are in non-proprietary text format, you can edit them with any text editor, and assure their continuity and crossplatform compatibility.
It is much easier to query documents since their semantic components are structurally tagged.
Advantages of DocBook
It is open source and platform-independent.
It is robust with about 400 elements for technical documentation (but also for general documentation).
It has a large worldwide base of users and an international network of peer-to-peer support.