The DocBook XSL stylesheets provide a serie of ready-to-use templates to
process documents based on the DocBook XML DTD. They can generate different
types of output files, like XHTML, slides, manpages, JavaDoc...

They are written in a modular fashion. Each of the HTML and FO stylesheets
starts with a driver file that assembles a collection of component files
into a complete stylesheet. This modular design puts similar things together
into smaller files that are easier to write and maintain than one big
stylesheet.