JSON Schema MWE: $ref vs sibling keywords (Ruby)

jsonschema_ref_vs_siblings.rb

gem 'json-schema'
require 'json-schema'

schema = <<~SCHEMA
    {
      "$schema": "http://json-schema.org/draft-04/schema#",
      "title": "A test schema",
      "type": "object",
      "oneOf": [
        {
          "properties": {
            "type": {
              "$ref": "#/definitions/foo",
              "enum": ["a"]
            },
            "name": {
              "type": "string"
            }
          },
          "required": ["type", "name"]
        },
        {
          "properties": {
            "type": {
              "$ref": "#/definitions/foo",
              "enum": ["b"]
            },
            "id": {
              "type": "integer"
            }
          },
          "required": ["type", "id"]
        }
      ],
      "definitions": {
        "foo": {
          "type": "string",
          "enum": ["a", "b", "c"]
        }
      }
    }
    SCHEMA

puts JSON::Validator.fully_validate(schema, '{ "type": "a", "id": 77 }')