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From Unreal Wiki, The Unreal Engine Documentation Site
This is the Tournament DarkMatch game type. It uses maps with the prefix "TDK" and the MapList class Botpack.TDKMapList.
This is a hidden UT gametype. There are no maps for it, but if you want to see how it works rename a DM map to TDK and add the following line to the [Public] section of your Botpack.int:
Note: This gametype has no connection to any DarkMatch mutator.