code: function ImportantDate(obj){
      this._id = obj && obj.id;
      this._tag = obj && obj.tag;
      this._date = obj && obj.date;
  }
docs: Contact Important Date information
  @typedef {Object} Contact.ImportantDate
  @property {string} tag - The context tag associated with this date
  @property {dateTime} date - An important date for this contact, as an ISO 8601 timestamp