extensions in docbook-xsl-ns-1.73.1

I downloaded  docbook-xsl-ns-1.73.1.tar.bz2 on 20th august, and there no extension directory,
while docbook-xsl-1.73.1.tar.bz2 does contain the directory 
   Ian W Moor                    Department of Computing,
           Imperial College.
                                    180 Queensgate
                                     London SW7 2AZ UK.