What I can't seem to accomplish is sorting the resulting pairs into
numerical order based on the first and then the second values in each
pair. Like this (this line breaks are just for visual clarity in this
email and are not necessary in the transform):

"1 0", "1 1", "1 2", "1 3", "1 4", "2 0", "2 1", "2 3", "2 4", "5 0", "6 0", "10 0", "10 1", "10 2"

<xsl:for-each select="$result">
   <xsl:sort select="tokenize(., ' ')[1]" data-type="numeric" />
   <xsl:sort select="tokenize(., ' ')[2]" data-type="numeric" />
   .... do your thing ...
</xsl:for-each>

Cheers,
-- Abel Braaksma