[xsl] Finding an element without a particular attribute?

["dvint@xxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

I'm processing content produced with json-to-xml(). So there are a buch 
of <map> elements. Many have the @key attribute and are easy to match. 
I'm drawing a blank on how to find map elements without the @key.

<map key="mime">
   <string key="type">array</string>
   <array key="items">
      <map>
         <string key="type">string</string>
      </map>
   </array
   </map>
<map key="uri">
   <string key="type">string</string>
</map>
<map key="doctype">
   <string key="type">string</string>
</map>


Any thoughts? I tried map[@key=''] with no luck.

..dan