 "field": "y1" },
              "z": { "value": 5.5 },
              "z2": { "value": 5.5 }
            }
          }
        },
        {
          "type": "rect",
          "from": { "data": "leaves" },
          "encode": {
            "enter": {
              "stroke": { "value": "#fff" },
              "opacity": { "value": 0.2 }
            },
            "update": {
              "x": { "field": "x0" },
              "y": { "field": "y0" },
              "x2": { "field": "x1" },
              "y2": {