Add attribute to root node

I have a quite simple question but I am doing somethings wrong. How can
I just add a schema association attribute to the root node of a
document?

When I do this no attribute will appear.

	<xsl:template match="/">
		<xsl:copy>
			<!-- add association to general kiwi validator
xsd -->
			<xsl:attribute
name="xsi:noNamespaceSchemaLocation">
				<xsl:value-of select="$validator-url"/>
			</xsl:attribute>

			<xsl:copy-of select="@*"/>
			<xsl:apply-templates />
		</xsl:copy>
	</xsl:template>

Robert