The xsl:sort element define a sort key. This sort key determines
the order in which selected nodes are processed by the xsl:for-each
A D V E R T I S E M E N T
A sort can be done more than one xsl:sort element. Each sort is applied in
the order in which it occurs. Duplicate values are left in document order. After
the first sort has reordered the nodes, the second sort is applied to any nodes
that had duplicate values in the first sort. The third sort is applied to any
nodes that had duplicate values in the second sort, and so on.