SharePoint MembersWebPartDisplayType

Displays members of a WebPartZone in a document workspace home page. Membership is displayed as a list, by using the SPList class.

WebUserGroups – Indicates that the member of a WebPartZone is in the collection of user objects that are explicitly assigned permissions to access the Web site.    
WebMemberGroup – Indicates whether this site is in a special group, based on AllProperties metadata of the site.    
GroupMembership – Indicates that the member of a WebPartZone is in a collection of group objects.  This collection is associated with a collection of user objects that are displayed on the Web site.