<func:function name="mime:split64">
    <xsl:param name="str"/>
    <func:result>
      <xsl:value-of select="concat(substring($str,1,76),$CRLF)"/>
      <xsl:if test="string-length($str) > 76">
        <xsl:value-of select="mime:split64(substring($str,77))"/>
      </xsl:if>
    </func:result>
  </func:function>