allow to override is_primary result using an argument given to object constructor (have to be given to 'initargs' argument of .render like initargs={'is_primary': False}
"""this contains the cube-specific entities' classes
:organization: Logilab
:copyright: 2001-2009 LOGILAB S.A. (Paris, FRANCE), license is LGPL v2.
:contact: http://www.logilab.fr/ -- mailto:contact@logilab.fr
:license: GNU Lesser General Public License, v2.1 - http://www.gnu.org/licenses
"""