Early manuscript draft
XML is first and foremost a document format. It was always intended for web pages, books, scholarly articles, poems, short stories, reference manuals, tutorials, texts, legal pleadings, contracts, instruction sheets, and other documents that human beings would read. Its use as a syntax for computer data in applications like syndication, order processing, object serialization, database exchange and backup, electronic data interchange, and so forth is mostly a happy accident.
DocBook (http://www.docbook.org/) is an
SGML application designed for new documents, not old ones.
It's especially common in computer documentation. Several
O'Reilly books have been written in DocBook including
http://www.linuxdoc.org/) corpus is written in
DocBook.