Compute attribute value from sub-element

Suppose I had the following XML fragment:

    <entry>
      <key>foo</key>
      <description>A sample link</description>
    </entry>

Suppose I would like to create the following output using XT:

    <a href="http://www.frob.org/search?type=simple&key=foo">A sample link</a>

How would I go about this?  My problem is how to create the `href'
attribute of the output element `a', in particular how to concat the
constant string "http://www.frob.org/search?type=simple&key=" and the
content of the `key' input element.

tia,
kai
-- 
I like BOTH kinds of music.


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