code: @SuppressWarnings("unchecked")
    protected ValueBoxBase<E> getTextBoxFromEvent(final GwtEvent<?> pevent) {
      final ValueBoxBase<E> ptextBox;
      if (pevent.getSource() instanceof SuggestBox) {
        ptextBox = (ValueBoxBase<E>) ((SuggestBox) pevent.getSource()).getValueBox();
      } else if (pevent.getSource() instanceof ValueBoxBase<?>) {
        ptextBox = (ValueBoxBase<E>) pevent.getSource();
      } else {
        throw new RuntimeException("Widget type not supported!");
      }
      return ptextBox;
    }
docs: get ValueBoxBase which produced the event.
  
  @param pevent event to get box from
  @return ValueBoxBase