+** If User X *can_write* role A, and role A *can_read* Object B, then User X *can_read* Object B.
+** If User X *can_read* role A, and role A *can_write* Object B, then User X *can_read* Object B.
+
+h2. Projects and Roles
+
+A "project" is a subtype of Group that is displayed as a "Project" in Workbench, and as a directory by @arv-mount@.
+* A project can own things (appear in @owner_uuid@)
+* A project can be owned by a user or another project.
+* The name of a project is unique only among projects and filters with the same owner_uuid.
+* Projects can be targets (@head_uuid@) of permission links, but not origins (@tail_uuid@). Putting a project in a @tail_uuid@ field is an error.
+
+A "filter" is a subtype of Group that is displayed as a "Project" in Workbench, and as a directory by @arv-mount@. See "the groups API documentation":{{ site.baseurl }}/api/methods/groups.html for more information.
+* A filter group cannot own things (cannot appear in @owner_uuid@). Putting a filter group in an @owner_uuid@ field is an error.
+* A filter group can be owned by a user or a project.
+* The name of a filter is unique only among projects and filters with the same owner_uuid.
+* Filters can be targets (@head_uuid@) of permission links, but not origins (@tail_uuid@). Putting a filter in a @tail_uuid@ field is an error.
+
+A "role" is a subtype of Group that is treated in Workbench as a group of users who have permissions in common (typically an organizational group).
+* A role cannot own things (cannot appear in @owner_uuid@). Putting a role in an @owner_uuid@ field is an error.
+* All roles are owned by the system user.
+* The name of a role is unique across a single Arvados cluster.
+* Roles can be both targets (@head_uuid@) and origins (@tail_uuid@) of permission links.
+* By default, all roles are visible to all active users. However, if the configuration entry @Users.RoleGroupsVisibleToAll@ is @false@, visibility is determined by normal permission rules, _i.e._, a role is only visible to users who have that role, and to admins.
+* By default, any user can create a new role. However, if the configuration entry @Users.CanCreateRoleGroups@ is @false@, only admins can create roles.