code: protected void addErrorMessage(String message)
  	{
  		fErrorMessages.remove(message);
  		fErrorMessages.add(message);
  		setErrorMessage(message);
  		setValid(message == null);
  	}
docs: Adds the given error message to the errors currently displayed on this page. The page displays the most recently
  added error message. Clients should retain messages that are passed into this method as the message should later
  be passed into removeErrorMessage(String) to clear the error. This method should be used instead of
  setErrorMessage(String).
  
  @param message
  the error message to display on this page.