If the bones are present in the rigging an item containing only a single group will be affected by the group(s) before or after it in the hierarchy. In  other words a piece of clothing grouped to the chest (in most rigging configureations) will be affected by the abdoment group, the neck and the l&r collar group, AS LONG AS THE RIG CONTAINS THE BONES FOR THOSE GROUPS. Obviously if there are no bones for those groups they will be ignored. Another common use of this is the shoe. in most cases if the shoe only "covers" the thigh, foot and toe groups it can a be placed in the Foot group, if the CR3 file contains the shin, foot and toe bones these will affect the shoe as well.

mike