json_schema: {
      "$schema": "http://json-schema.org/draft-07/schema#",
      "definitions": {
          "foo.Date": {
              "properties": {
                  "day": {
                      "type": "number"
                  },
                  "month": {
                      "type": "number"
                  },
                  "year": {
                      "type": "number"
                  }
              },
              "type": "object"
          }
      },
      "properties": {
          "date": {
              "$ref": "#/definitions/foo.Date"
          }
      },
      "required": [
          "date"
      ],
      "type": "object"
  }