Getting the value of the browser selector

I can't see how to get the value of the browser selector into a 
parameter inside a map:transform in my sitemap.xmap.

The example I found shows how to push different transforms according to 
the value, eg

   <map:select type="browser">
     <map:when test="msie8">
       <map transform src="foo.xsl">
         <map:parameter name="browser" value="msie8"/>
       </map:transform>
     </map:when>
   ...etc...
   </map:select>

but that's a very long-winded, manual, and hard-coded way round. Is 
there a curly-brace syntax that would let me say

   <map:parameter name="browser" value="{something:browser}"/>

and simply have it pass the value to the XSLT stylesheet?

The selector for "browser" doesn't seem to have an "else" or default 
value. What happens when the user-agent string goes unmatched?

///Peter