code: protected ValidationListener registerGuarded(String propertyName, Guarded guarded) {
  		GuardedValidationListener guardedValidationListener = new GuardedValidationListener(propertyName, guarded);
  		validationResults.addValidationListener(propertyName, guardedValidationListener);
  		guardedValidationListener.validationResultsChanged(validationResults);
  		return guardedValidationListener;
  	}
docs: Register a guarded object on a specific property. To keep things in sync,
  it also triggers a first time check. (validationResultsModel can already
  be populated)
  
  @param propertyName property to listen for.
  @param guarded component that needs guarding.
  @return {@link ValidationListener} created during the process.