<xsl:for-each select="/article/keywords/keyword">
  <xsl:variable name="kw" select="."/>
    <a href="/search.php?keyword={$kw}" title="{$kw}">
       <xsl:value-of select="$kw" />
    </a>
  <xsl:if test="position()!=last()">, </xsl:if>
</xsl:for-each>

<?xml version="1.0" encoding="UTF-8"?>
<article>
   <keywords>
      <keyword>Cascading Style Sheet</keyword>
      <keyword>Hypertext Markup Language</keyword>
   </keywords>
</article>