used within an xsl:for-each or xsl:apply-templates or saxon:group element
attributes:
select: default to "."
order: "ascending" or "descending", default "ascending"
data-type: build in type
collation
case-order: "upper-first" or "lower-first only used when data-type is "text"
lang: base on java system locale
example:
<xsl:apply-templates select="BOOK">
<xsl:sort select="AUTHOR"/>
<xsl:sort select="@DATE" order="descending" lang="GregorianDate"/>
</xsl:apply-templates>
<xsl:perform-sort>
returns a sorted sequence
<xsl:perform-sort select=expression>
<!-- Content: (xsl:sort+, sequence-constructor) -->
</xsl:perform-sort>