       SippShowBackFaces [flag]
              This command can be used if backface culling should
              not be performed. If the boolean flag is true back-
              facing  polygons are "inverted" (their surface nor-
              mal is negated) and then rendered. This  is  useful
              if  an object description does not use a consequent
              ordering of the vertices.  This also controls  hid-
              den  line  elimination  when  doing line rendering.
              The rendering step can be slowed down  considerably
              since,  on the average, twice as many polygons need
              to  be  rendered.  The  default  is  that  backface
              culling  should  be  performed (false).  If flag is
              not specified, the current value is returned.
