code: public TimezoneId setTimezoneId(String timezoneId) {
  		TimezoneId prop = (timezoneId == null) ? null : new TimezoneId(timezoneId);
  		setTimezoneId(prop);
  		return prop;
  	}
docs: Sets an ID for this timezone. This is a <b>required</b> property.
  @param timezoneId the timezone ID or null to remove
  @return the property that was created
  @see <a href="http://tools.ietf.org/html/rfc5545#page-102">RFC 5545
  p.102-3</a>
  @see <a href="http://tools.ietf.org/html/rfc2445#page-97">RFC 2445
  p.97-8</a>