code: public static AirlineCheckinTemplateBuilder addAirlineCheckinTemplate(
  			String introMessage, String locale, String pnrNumber,
  			String checkinUrl) {
  		return new AirlineCheckinTemplateBuilder(introMessage, locale,
  				pnrNumber, checkinUrl);
  	}
docs: Adds an Airline Checkin Template to the response.
  
  @param introMessage
  the message to send before the template. It can't be empty.
  @param locale
  the current locale. It can't be empty and must be in format
  [a-z]{2}_[A-Z]{2}. Locale must be in format [a-z]{2}_[A-Z]{2}.
  For more information see<a href=
  "https://developers.facebook.com/docs/internationalization#locales"
  > Facebook's locale support</a>.
  @param pnrNumber
  the Passenger Name Record number (Booking Number). It can't be
  empty.
  @param checkinUrl
  the url for the checkin. It can't be empty.
  @return a builder for the response.
  @see <a href=
  "https://developers.facebook.com/docs/messenger-platform/send-api-reference/airline-checkin-template"
  > Facebook's Messenger Platform Airline Checkin Template
  Documentation</a>