There has been a lot of press recently about XML, and DocBook support for XML. DocBook is a collection of markup tags that follow a specified hierarchy. XML DocBook v4.1.2 is now officially supported by the LDP. If you're familiar with SGML and want to convert to XML, please keep the following in mind (list borrowed from DocBook: The Definitive Guide):
All XML markup is case sensitive. All element, attribute, and entity names have to be in lowercase. SGML is not case sensitive.
All attributes have to be quotes using either straight (') or double (") quotes.
Empty elements (like xref) have to end with a /: <xref/>.
Tag minimizations (</>) are not supported. The LDP discourages their use in SGML as well.