{
  "$schema": "urn:prism:schema:v1:spec",
  "title": "Nested facet (region then brand then quarter score)",
  "data": {
    "name": "samples",
    "values": [
      {"region": "NA", "brand": "alpha", "qtr": "Q1", "score": 0.42},
      {"region": "NA", "brand": "alpha", "qtr": "Q2", "score": 0.45},
      {"region": "NA", "brand": "beta",  "qtr": "Q1", "score": 0.51},
      {"region": "NA", "brand": "beta",  "qtr": "Q2", "score": 0.55},
      {"region": "EU", "brand": "alpha", "qtr": "Q1", "score": 0.31},
      {"region": "EU", "brand": "alpha", "qtr": "Q2", "score": 0.36},
      {"region": "EU", "brand": "beta",  "qtr": "Q1", "score": 0.49},
      {"region": "EU", "brand": "beta",  "qtr": "Q2", "score": 0.52}
    ]
  },
  "facet": {"row": {"field": "region", "type": "nominal"}},
  "spec": {
    "$schema": "urn:prism:schema:v1:spec",
    "facet": {"column": {"field": "brand", "type": "nominal"}},
    "spec": {
      "$schema": "urn:prism:schema:v1:spec",
      "mark": "bar",
      "encoding": {
        "x": {"field": "qtr",   "type": "nominal"},
        "y": {"field": "score", "type": "quantitative"}
      }
    }
  }
}