# xsl:perform-sort

The `xsl:perform-sort` instruction takes a sequence as its input and produces a sorted sequence as its output.

The input sequence may be specified either using the `select` attribute, or using the instructions contained within the `xsl:perform-sort` instruction.

The sort criteria are specified using `xsl:sort` elements as children of `xsl:perform-sort`, in the usual way.

For example:

    <xsl:perform-sort select="//BOOK">
        <xsl:sort select="author/last-name"/>
        <xsl:sort select="author/first-name"/>
    </xsl:perform-sort>

It's often useful to use `xsl:perform-sort` inside a stylesheet function; the function can return the sorted sequence as its result, and can be invoked directly from an XPath expression.

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