{
  "model":
  {
    "stage":
    { "view":   "stage",
      "width":  "@width",
      "height": "@height"
    },

    "birds":
    [ { "@count": 500,
        "view":   [ "@some", "tux", "owl"],
        "r":      { "@min":  25, "@max": 40 },
        "x":      { "@min": 0.2, "@max": 0.8, "@relative": "@width" },
        "y":      { "@min": 0.2, "@max": 0.8, "@relative": "@height" },
        "vx":     { "@min": 100, "@max": 300, "@positive": 0.5 },
        "vy":     { "@min": 100, "@max": 300, "@positive": 0.5 }
      }
    ]
  },

  "view":
  {
    "stage": { "resource": "background" },
    "owl":   { "resource": "owl", "r": "@birdRadius" },
    "tux":   { "resource": "tux", "r": "@birdRadius" }
  }
}