code: static void capturePageEvent(String eventName, final EventHandler handler) {
      HtmlPlatform.captureEvent(eventName, new EventHandler() {
        @Override
        public void handleEvent(NativeEvent evt) {
          handler.handleEvent(evt);
        }
      });
    }
docs: Capture events that occur anywhere on the page.
  <p>
  Note that event values will be relative to the page (not the
  rootElement) {@see #getRelativeX(NativeEvent, Element)} and {@see
  #getRelativeY(NativeEvent, Element)}.