A formatting class provided by the Text::Diff module, to add XHTML
markup to the unified diff format.

In the XHTML formatted by this module, the contents of the diff
returned by diff() are wrapped in a <div> element, as is each hunk
of the diff. Within each hunk, all content is properly HTML encoded
using HTML::Entities, and the various sections of the diff are marked
up with the appropriate XHTML elements.