xref inside citation

["Deepak K. Shrestha" <d888pak@netscape.net>]

Hi,

I have posted same related question in docbook-apps (I think wrong place 
  to post) reference: 
http://sources.redhat.com/ml/docbook-apps/2004-q4/msg00573.html

My Question is:

Is <xref> tag allowed inside <citation>?

thanks in advance.

Deepak K. Shrestha