> <xsl:key name="p" match="*">
> <xsl:number level="any" count="*" from="/"/>
> </xsl:key>

This creates a key of elements-by-position, so given a number it will
return the element at that position.

> <xsl:variable name="posn">
>   <xsl:number level="any" count="*" from="/"/>
> </xsl:variable>

This gets the position of the context node.  (this could do with an
as="xs:integer")

> <xsl:variable name="val" select="document($src)/key('p', $posn)"/>

This gets the value of the of the element at that position in document($src)


--
Andrew Welch
http://andrewjwelch.com
Kernow: http://kernowforsaxon.sf.net/