{
  "$schema": "urn:prism:schema:v1:spec",
  "title": "Cumulative volume",
  "data": {
    "name": "volume",
    "values": [
      {"day": "2026-01-01", "vol": 100},
      {"day": "2026-01-02", "vol": 175},
      {"day": "2026-01-03", "vol": 240}
    ]
  },
  "mark": "area",
  "encoding": {
    "x": {"field": "day", "type": "temporal"},
    "y": {"field": "vol", "type": "quantitative"}
  }
}