Rewriting
Rewriting is a convenient method of moving an entire tree
<rewriteSystem systemIdStartString="http://www.w3.org/"
rewritePrefix="/projects/w3c/WWW/"/>
This entry would map:
http://www.w3.org/2002/xmlspec/dtd/2.3/xmlspec.dtd
to
/projects/w3c/WWW/2002/xmlspec/dtd/2.3/xmlspec.dtd