FO: Cross references in books

I made an <xref> element with an "idref" attribute in my DTD. Then some
block elements have "id" attributes. I thought this would be handy when I
do cross-references, like in:

<p>Read more about Iraq on page <xref idref="iraq"/>.</p>

I'm trying to implement an <xref> template in XSL-FO now, but with no luck
so far. I don't know how to extract the page number on the other page.
Maybe it's not possible?

Gustaf


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