'Called once for each user-usable plot mode.
For Cartesian2D, it is invoked after the
class definition: Cartesian2D._register()'

@classmethod
def _register(cls):

    name = cls.__name__
    cls._init_mode()
    try:
        (i, d) = (cls.i_var_count, cls.d_var_count)
        for a in cls.aliases:
            if (a not in PlotMode._mode_alias_list):
                PlotMode._mode_alias_list.append(a)
            PlotMode._mode_map[d][i][a] = cls
        if cls.is_default:
            PlotMode._mode_default_map[d][i] = cls
    except Exception as e:
        raise RuntimeError(('Failed    to    register    plot    mode    %s.    Reason:    %s' % (name, str(e))))
