code: function stringifyProperty (value, propDefinition) {
    // This function stringifies but it's used in a context where
    // there's always second stringification pass. By returning the original
    // value when it's not an object we save one unnecessary call
    // to JSON.stringify.
    if (typeof value !== 'object') { return value; }
    // if there's no schema for the property we use standar JSON stringify
    if (!propDefinition || value === null) { return JSON.stringify(value); }
    return propDefinition.stringify(value);
  }
docs: Serialize a single property.