code: 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')
docs: 2-element list of ints : Dimensions of the viewport
  
          The viewport is a bounding box containing the visualization. If the
          dimensions of the visualization are larger than the viewport, then
          the visualization will be scrollable.
  
          If undefined, then the full visualization is shown.