master.xml

<data>
  <products>
    <entry>one</entry>
        <entry>two</entry>
        <entry>three</entry>
        <entry>four</entry>
  </products>
</data>

master.xsl

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">

  <xsl:output method="xml" indent="yes" />

  <xsl:template match="/">
    <hi>
      <xsl:value-of select="data/products/entry[position() mod 4 = 1]" mode="group" />
    </hi>
  </xsl:template>

  <xsl:template match="products/entry" mode="group">
    <xsl:variable name="group">
      <xsl:call-template name="num-to-word">
        <xsl:with-param name="num-to-word" select="position()"/>
      </xsl:call-template>
    </xsl:variable>
    <div class="group {$group}">
      <xsl:apply-templates select=". | following-sibling::entry[position() &lt; 4]" mode="navigation"/>
    </div>
  </xsl:template>


  <xsl:template match="products/entry | products/entry" mode="product">
    <article class="product"></article>
  </xsl:template>
  
  <xsl:template name="num-to-word">
    <xsl:param name="num"/>

    <xsl:choose>
        <xsl:when test="$num = 1">one</xsl:when>
        <xsl:when test="$num = 2">two</xsl:when>
        <xsl:when test="$num = 3">three</xsl:when>
        <xsl:when test="$num = 4">four</xsl:when>
        ...
    </xsl:choose>
  </xsl:template>
</xsl:stylesheet>