citation and xref confusion

Hi,

My Short question is: Is <xref> tag inside <citation> allowed in DocBook???

My Long description about why I am asking this question is:

---------------------
I want to insert <xref> inside <citation> to produce my bibliography
citation inside the brackets, which is something like

<citation>
   <xref linkend ="DKS2001"/>
</citation>

<biblioentry id="DKS2001" xreflabel="Deepak et.al. 2001">
...
...
</biblioentry>

to produce something like [Deepak et.al. 2001] in my output. I tried
using simply <xref> in my paragraphs (as suggested in DocBook XSL book
by Bob Stayton) but generated text is not inside bracket. Since only
citation seems to produce this brackets, I want to insert <xref> inside
<citation> to produce the desired result.

My problem is, i am using Morphon 3.1.4 editor and it doesn't allow me
to insert the <xref> inside <citation> (only before <citation> or
after). That seems like <xref> inside the <citation> is not allowed
according to DocBook DTD (I am using v4.3). But inserting the <xref>
after <citation> and dragging it inside citation (in tree view) seems to
be ok (and Morphon doesn't complain ????? I don't know why). Saving the
documents and processing with Saxon and FOP produces the desired result
without any complain. Why is that so? Although I have found the
workaround with my editor, I just want to make sure if it is ok before
proceeding with citing my bibliography entries.

thanks in advance

Deepak K. Shrestha