PK_ERROR_code_t   PK_GROUP_create_from_entities
(
--- received arguments ---
PK_PART_t         part,             --- part within which group is to be
                                    --- created
PK_CLASS_t        entity_class,     --- allowed class of entities in group
int               n_entities,       --- number of entities  (>=0)
const PK_ENTITY_t entities[],       --- entities

--- returned arguments ---
PK_GROUP_t *const group             --- group created
)


This function creates a group within the given part containing the given
set of entities.


Specific Errors:
    PK_ERROR_wrong_group_class      this part may not have a group with this
                                    entity class
    PK_ERROR_invalid_group_class    not allowed as a group's entity class
    PK_ERROR_wrong_class_for_group  entity is of a class not allowed in
                                    this group
    PK_ERROR_not_in_same_part       some entity is not within the part


Groups within a body may contain entities of one of the following classes:

    PK_CLASS_face
    PK_CLASS_edge
    PK_CLASS_vertex
    PK_CLASS_surf
    PK_CLASS_curve
    PK_CLASS_point
    PK_CLASS_region
    PK_CLASS_entity   each entity may be of any of those classes above

All the entities in a group within a body must themselves belong to that
body.  For geometric entities, the entity may either be attached to a
topological entity of the body, or be construction geometry of the body.

Groups within an assembly may contain entities of one of the following
classes:

    PK_CLASS_instance
    PK_CLASS_surf
    PK_CLASS_curve
    PK_CLASS_point
    PK_CLASS_entity  each entity may be of any of those classes above

The only surfaces, curves and points allowed in a group within an assembly are
construction geometry owned by the assembly.  Instances in a group within
an assembly must themselves be owned by that assembly.