docs: public void addForwardedField(int input, int sourceField, int targetField) {
  
  		Map<Integer, FieldSet> fieldMapping;
  
  		if (input != 0 && input != 1) {
  			throw new IndexOutOfBoundsException();
  		} else if (input == 0) {
  			fieldMapping = this.fieldMapping1;
  		} else {
  			fieldMapping = this.fieldMapping2;
  		}
  
  		if(isTargetFieldPresent(targetField, fieldMapping)) {
  			throw new InvalidSemanticAnnotationException("Target field "+targetField+" was added twice to input "+input);
  		}
  
  		FieldSet targetFields = fieldMapping.get(sourceField);
  		if (targetFields != null) {
  			fieldMapping.put(sourceField, targetFields.addField(targetField));
  		} else {
  			fieldMapping.put(sourceField, new FieldSet(targetField));
  		}
  	}