code: function shouldBeUpdated(target, propertyName, json) {
    return (
      json[propertyName] !== undefined && // Must have a value to update to
      propertyName.length > 0 && // Must have a name to update
      propertyName[0] !== "_" && // Must not be a private property
      (propertyName !== "id" || !defined(target.id))
    ); // Must not be overwriting 'id'
  }
docs: Determines whether this property is valid for updating.