def lookup_json_pointer(ref)
      elements = ref.split('/')
      elements.shift
      @schema.dig(*elements) || raise("Definition `#{ref}` not found in the schema")
    end
def lookup_json_pointer(ref)
      elements = ref.split('/')
      elements.shift
      @schema.dig(*elements) || raise("Definition `#{ref}` not found in the schema")
    end
Look up a "pointer" like "#/definitions/title" in the schema.