<xsl:stylesheet
  version="1.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:msxsl="urn:schemas-microsoft-com:xslt"
  xmlns:my="http://example.com/2008/my"
  exclude-result-prefixes="msxsl my">

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

  <msxsl:script implements-prefix="my" language="C#">
    public XPathNodeIterator stringToCodepoints(string str)
    {
      XmlDocument doc = new XmlDocument();
      using (XmlWriter writer = doc.CreateNavigator().AppendChild())
      {
        writer.WriteStartElement("characters");
        foreach (char c in str)
        {
          writer.WriteElementString("char", string.Format("{0}", (int)c));
        }
        writer.WriteEndElement();
      }
      return doc.CreateNavigator().Select("characters/char");
    }
  </msxsl:script>

  <xsl:template match="/">
    <example>
      <xsl:for-each select="my:stringToCodepoints('abcd')">
        <codepoint>
          <xsl:value-of select="."/>
        </codepoint>
      </xsl:for-each>
    </example>
  </xsl:template>
</xsl:stylesheet>