UnrealTournament Mutators are arguably one of the strongest features available for customizing the game. UT allows you to set up a list of Mutators for the games you play, using the Mutators button in the Start Game windows. Unfortunately, there are now so many Mutators available, some doing very specific jobs, that loading the same set of Mutators for every game really isn't appropriate.
XMaps solves this problem by allowing you to set up two additional lists of Mutators - those that are always loaded for Game Types, and those that are loaded with Extended map lists. So, you can set up a hierarchical loading of Mutators as follows:
Many XMaps users create a few Extended map lists containing maps that have related features (maps set in space or outside, for example) just so they can always have the same set of Mutators running in those maps. You can almost create a custom game environment on your server by grouping related maps and Mutators this way.

The Mutators page only contains one configuration control - the button that opens the XMaps Mutators editing window. The number of Mutators that you've set up in XMaps for the currently selected game type is shown underneath the button. If you want XMaps to load some Mutators for a specific game type, click the Mutators button and make your choices.
If you've uninstalled a game type or mod, then the Purge Unused Lists button may be enabled. Use this button to remove any Mutator lists for the uninstalled games, to free up the space those lists are taking. If Purge Unused Lists is disabled, then all the Mutator lists that are set up are for Game Types XMaps knows about. See Game Types for more information.
How do the Mutators Load?When XMaps is running, it'll load all the Mutators you've selected if (a) they're not already running, and (b) UT won't be loading them. All XMaps' Mutator lists cooperate with each other and any list of Mutators set up in UT.
If you also want to load some Mutators along with an Extended map list, set them up in the Extended Lists Game Options page.
Of course, XMaps can only load your Mutators when it's already running - there's no point adding XMaps itself to any XMaps Mutators lists, as it has to be loaded to read the lists in the first place... XMaps should be loaded as described in Running XMaps.