code: function Alert(properties) {
              this.activePeriod = [];
              this.informedEntity = [];
              if (properties)
                  for (var keys = Object.keys(properties), i = 0; i < keys.length; ++i)
                      if (properties[keys[i]] != null)
                          this[keys[i]] = properties[keys[i]];
          }
docs: Properties of an Alert.
  @memberof transit_realtime
  @interface IAlert
  @property {Array.<transit_realtime.ITimeRange>|null} [activePeriod] Alert activePeriod
  @property {Array.<transit_realtime.IEntitySelector>|null} [informedEntity] Alert informedEntity
  @property {transit_realtime.Alert.Cause|null} [cause] Alert cause
  @property {transit_realtime.Alert.Effect|null} [effect] Alert effect
  @property {transit_realtime.ITranslatedString|null} [url] Alert url
  @property {transit_realtime.ITranslatedString|null} [headerText] Alert headerText
  @property {transit_realtime.ITranslatedString|null} [descriptionText] Alert descriptionText
  @property {transit_realtime.ITranslatedString|null} [ttsHeaderText] Alert ttsHeaderText
  @property {transit_realtime.ITranslatedString|null} [ttsDescriptionText] Alert ttsDescriptionText
  @property {transit_realtime.Alert.SeverityLevel|null} [severityLevel] Alert severityLevel
   
  Constructs a new Alert.
  @memberof transit_realtime
  @classdesc Represents an Alert.
  @implements IAlert
  @constructor
  @param {transit_realtime.IAlert=} [properties] Properties to set