for each:每3项获取一次(分成3列)

xsl中有以下节点:

<foo>
    <bar>1</bar>
    <bar>2</bar>    
    <bar>3</bar>
    <bar>4</bar>        
    <bar>5</bar>
    <bar>6</bar>    
    <bar>7</bar>
    <bar>8</bar>            
    <bar>9</bar>
</foo>

<ul class="one">
    <li>1</li>
    <li>4</li>
    <li>7</li>
</ul>
<ul class="two">
    <li>2</li>
    <li>5</li>
    <li>8</li>
</ul>
<ul class="three">
    <li>3</li>
    <li>6</li>
    <li>9</li>
</ul>

很难弄清楚如何循环并获取第三个项目,希望执行以下操作:

<ul class="one">
<xsl:for-each select="exlt:node-set($blah)/foo/bar[X1]">
    <li><xsl:value-of select="node()"/></li>
</xsl:for-each>
</ul>

<ul class="two">
<xsl:for-each select="exlt:node-set($blah)/foo/bar[X2]">
    <li><xsl:value-of select="node()"/></li>
</xsl:for-each>
</ul>

<ul class="three">
<xsl:for-each select="exlt:node-set($blah)/foo/bar[X3]">
    <li><xsl:value-of select="node()"/></li>
</xsl:for-each>
</ul>   

Where:
X1 = Every third item starting from position 1
X2 = Every third item starting from position 2
X3 = Every third item starting from position 3