This is a minimal version of the DocBook XSL Style Sheet
distribution, which you can download from
http://docbook.sourceforge.net/.

Nothing is modified in these files, all files are left untouched,
so these are the same ones you can find in the distribution. We
omitted some files and directories though, and only left those that
we use for output generation.

The reason to put this to phpdoc was to encourage compatibility,
so we don't need to force users to have a specific version of
the XSL style sheets locally, but we can still rely on a version
of the sheets we tested our customizations with.