{
    "$schema": "http://json-schema.org/draft-04/schema#",
    "allOf": [
        {
            "$ref": "#/definitions/yesno"
        }
    ],
    "enum": [
        "yes"
    ],
    "definitions": {
        "yesno": {
            "type": "string",
            "enum": [
                "yes",
                "no"
            ]
        }
    }
}