@grammar(list)
    def viewport(value):
        if len(value) != 2:
            raise ValueError('viewport must have 2 dimensions')
        for v in value:
            _assert_is_type('viewport dimension', v, int)
            if v < 0:
                raise ValueError('viewport dimensions cannot be negative')
2-element list of ints : Dimensions of the viewport
dataset/ETHPy150Open wrobstory/vincent/vincent/visualization.py/Visualization.viewport