By default, the Motion Mixer expects that a mix you create will affect the entire non-biped object. If you like, you can Filtering Mixer Tracks a trackgroup so clips in the mix affect only selected body parts. This functionality makes it easy for you to assign one set of XAF files to control the motion of an object's upper body, while another set controls the lower body.
For more information and procedures on the use of trackgroup filters, see Filtering Mixer Tracks.
The Trackgroup Filter dialog displays a list of objects, with the hierarchy indicated by indenting (if Subtree Display is on, which it is by default). Objects can be individually activated or deactivated by clicking them, or you can use the buttons across the bottom of the Trackgroup Filter diagram to expedite selections.
This list shows the scene's named selection sets. Choosing a set from this list selects its members in the Object list.