Distinct values in XSLT 1.0

XSLT 1.0

<xsl:key name="product" match="/items/item/products/product/text()" use="." />

<xsl:template match="/">

  <xsl:for-each select="/items/item/products/product/text()[generate-id()
                                       = generate-id(key('product',.)[1])]">
    <li>
      <xsl:value-of select="."/>
    </li>
  </xsl:for-each>

</xsl:template>