http://www.oasis-open.org/docbook/xml/simple/
The Simplified DocBook DTD is a small subset of the DocBook XML DTD. The online summary shows just how small this subset is.
This DTD is an attempt to make a small subset of DocBook. The goals of this subset are:
- Documents written in the subset must be 100% legal DocBook documents.
- This subset for single documents (articles, white papers, etc.), so there's no need for books or sets, just 'articles'.
- The markup should be the smallest practical subset, if you need richly structured markup, use full DocBook. In particular, the subset often selects a single element from a family of related elements; for example, programlisting is provided, but screen is not.
- The DTD must work in online browsers (it's XML not SGML). It must be small enough to download more-or-less painlessly.
Simplified DocBook: The Definitive Guide