'Lx-levels to load from the database = all levels down to the
lowest exposed level (L0=highest, L5=lowest)'

@property
def load_levels(self):

    load_levels = self._load_levels
    if (load_levels is None):
        load_levels = ('L0', 'L1', 'L2', 'L3', 'L4', 'L5')
        while load_levels:
            if (load_levels[(-1)] in self.levels):
                break
            else:
                load_levels = load_levels[:(-1)]
        self._load_levels = load_levels
    return load_levels
