why does new docbook RPM require openjade??

not sure if this is the right place to ask, but i just wanted to
upgrade my docbook-dtds RPM from 1.0.17 to 1.0.21 (RPM version
numbering), only to notice that the newest RPM has a dependency
on openjade that it didn't have before, so that the upgrade failed.

  in what way does the new DTD require openjade?  enquiring minds
want to know.

rday