To learn how xsl:sort works, I suggest you use xsl:value-of right after the statement that should be doing the sorting:

<xsl:sort select="some/Xpath">
<sort-by>
<xsl:value-of select="some/Xpath">
</sort-by>

XsltException: 'xsl:sort' cannot be a child of 'xsl:for-each' element.

Cheers,
-- Abel