Any ideas how to combine position and keys.

I have some documents that are tagged and I find the tagged documents using keys like this:

<xsl:key name="filtred_news" match="News" use="tags/XPathCheckBoxList/nodeId"/>
<xsl:param name="currentPage"/>

<xsl:template match="/">
    <xsl:apply-templates select="$currentPage/ancestor-or-self::Frontpage/Newslist">
        <xsl:with-param name="tags" select="macro/tags" />
        <xsl:with-param name="items" select="macro/items" />
    </xsl:apply-templates>
</xsl:template>

<xsl:template match="Newslist">
    <xsl:param name="tags" />
    <xsl:param name="items" />

    <ul class="news">
        <xsl:choose>
            <xsl:when test="string-length($tags) &gt; 0">
                <xsl:apply-templates select="key('filtred_news',$tags)" />
            </xsl:when>
            <xsl:otherwise>
                <xsl:apply-templates select="descendant::News[position() &lt;= $items]" />
            </xsl:otherwise>
        </xsl:choose>
    </ul>
</xsl:template>

If you see in the otherwise apply, I limit the number of outputs to 5 using a macro parameter.

How do I do the same when using keys ?