Upon matching attribute value, increment output

        If I have the following XML:
         
        <GRP>
          <CON @CODE="ABC"/>
          <CON @CODE="DEF"/>
          <CON @CODE="ABC"/>
          <CON @CODE="ABC"/>
          <CON @CODE="XYZ"/>
          <CON @CODE="ABC"/>
        </GRP>
         
        And I want my output to be:
         
        ABC
        DEF
        ABC_1
        ABC_2
        XYZ
        ABC_3
         
        How would I get there?  I cannot seem to manage it with any combination 
of count, value-of, match, etc., and almost all posts I see are for node values 
instead of attributes, or HTML instead of text...nothing I've seen seems to 
give me a valid idea to run with.
         
        Any help would be greatly appreciated!
         
        Thanks,
         
        Russ