json_schema: {
      "type": "object",
      "properties": {
          "foo": {
              "$ref": "#/definitions/Enum"
          }
      },
      "required": [
          "foo"
      ],
      "definitions": {
          "Enum": {
              "type": [
                  "number",
                  "boolean",
                  "string",
                  "null"
              ],
              "enum": [
                  0,
                  1,
                  null,
                  "str",
                  true
              ]
          }
      },
      "$schema": "http://json-schema.org/draft-04/schema#"
  }