XSL for-each: how to detect last node?

I have this simple code:

<xsl:for-each select="GroupsServed">
  <xsl:value-of select="."/>,<br/>
</xsl:for-each></font>

I'm trying to add a comma for each item added.

This has 2 flaws:

1. Case of when there's only 1 item: the code would unconditionally add a comma.
2. Case of when there's more than 1 item: the last item would have a comma to it.

What do you think is the most elegant solution to solve this?

I'm using XSLT 2.0

From stackoverflow ShaChris23

• If you're using XSLT 2.0, the canonical answer to your problem is

  <xsl:value-of select="GroupsServed" separator=", " />
  

  On XSLT 1.0, the somewhat CPU-expensive approach to finding the last element in a node-set is

  <xsl:if test="position() = last()" />
  

  ShaChris23 : thanks for the XSLT 1.0 approach. It worked fine on my 2.0

  Stobor : I shouldn't try to answer these questions via a phone. I've added the detail on the XSLT2.0 method, in case it wasn't clear earlier.
  From Stobor

• Final answer:

  <xsl:for-each select="GroupsServed">
    <xsl:value-of select="."/>            
    <xsl:choose>
      <xsl:when test="position() != last()">,<br/></xsl:when>
    </xsl:choose>
  </xsl:for-each>
  

  From ShaChris23