[xsl] key() now has 3 arguments ... right

[ihe onwuka <ihe.onwuka@xxxxxxxxxxxxxx>]

key() in an XSLT 2.0 pattern must have exactly two arguments

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform";
    version="2.0">

<xsl:key name="maindoc" match="person" use="@firstname"/>
<xsl:variable name="doc2" select="/"/>
<xsl:template match="key('maindoc','Sal',$doc2)">
    <xsl:value-of select="@firstname"/>
</xsl:template>

</xsl:stylesheet>

how come?