I have this bit of tal:

 <input type="hidden"
  
tal:condition="python:request.form.has_key('replyto')"
    
name="msg-1@inreplyto"
    tal:attributes="value
    
python:db.msg.get(request.form['replyto'].value,
            
'messageid')">

that I would like to have work.

-- rouilj