docs: public QRSCT reference(String reference) {
  		if (reference != null && reference.length() <= 35) {
  			this.text = ""; //$NON-NLS-1$
  			this.reference = checkValidSigns(reference);
  			return this;
  		}
  		throw new IllegalArgumentException("supplied reference [" + reference //$NON-NLS-1$
  				+ "] not valid: has to be not null and of max length 35"); //$NON-NLS-1$
  	}