code: 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"); //$NON-NLS-1$
  	}
docs: Sets the reference of this builder !!!If you set this attribute,
  attribute text will be reset to an empty string!!! It's only possible to
  define one of these attributes
  
  @param reference
  reference (max length: 35)
  @return QRSCT builder