> Is there some elegant way to use the correct xpath expression 
> depending 
> on the input document?
> 
> An "if then else" works if there's only two options, but I'll 
> have more 
> than that.
> 
> I suppose one obvious approach would be this ...
> 
> 	<xsl:variable name="citerefs" select="//db:biblioref/@linkend |
> 								
> 	//cite:biblioref/@cite:key |
> 								
> 	//tei:cit/@href"/>
> 


I would be inclined to do it with template rules:

<xsl:template match="db:biblioref">
  <xsl:apply-templates select="@linkend" mode="z"/>
</xsl:template>

<xsl:template match="cite:biblioref">
  <xsl:apply-templates select="@cite:key" mode="z"/>
</xsl:template>

<xsl:template match="@*" mode="z">
  ...
</xsl:template>

etc.

But perhaps I haven't understood the problem.

Michael Kay
http://www.saxonica.com/