varname question

Hi,
I have a situation where I want to refer to a variable name that looks like this:
_TYPEn_ where the 'n' is italicized to stand for some number, n. I tag it like this:
<varname>_TYPE<emphasis>n</emphasis>_</varname>

But I get this error when validating with onvdl:
test.xml:7:35: error: element "emphasis" from namespace "http://docbook.org/ns/docbook" not allowed in this context

I thought it was allowed to have emphasis in varname. What am I doing wrong?
thanks,
--Tim Arnold

DETAILS:
-----------------
<chapter xmlns="http://docbook.org/ns/docbook"
         xml:id="test" version="5.0">
  <info><title>la di da</title></info>
  <section>
    <info><title>hey</title></info>
    <para><varname>_TYPE<emphasis>n</emphasis>_</varname></para>
  </section>
</chapter>
-----------------
Here's the validation command:

/usr/local/bin/java -Dorg.apache.xerces.xni.parser.XMLParserConfiguration=org.apache.xerces.parsers.XIncludeParserConfiguration -jar /DocBook/oNVDL/bin/onvdl.jar /DocBook/V5.0/docbook.nvdl test.xml