vendor/github.com/go-openapi/spec/fixtures/more_circulars/item2.json

{
  "item": {
    "type": "object",
    "required": [
      "title"
    ],
    "properties": {
      "id": {
        "type": "integer",
        "format": "uint64",
        "readOnly": true
      },
      "title": {
        "type": "string",
        "minLength": 2,
        "maxLength": 80
      },
      "subitem": {
        "$ref": "#/item"
      }
    }
  }
}