def fill_opacity(value):
        """ValueRef : int or float, opacity of the fill (0 to 1)
        """
        if value.value:
            _assert_is_type('fill_opacity.value', value.value,
                            (float, int))
            if value.value < 0 or value.value > 1:
                raise ValueError(
                    'fill_opacity must be between 0 and 1')
ValueRef : int or float, opacity of the fill (0 to 1)