code: public void discardHeaderClick(ClickEvent event) {
          if (event == null) return;
  
          // Example: we use radioset on collapsible header, so stopPropagation() is needed
          // to suppress collapsible open/close behavior.
          // But preventDefault() is not needed, otherwise radios won't switch.
          // event.preventDefault(); // For example, clicked anchors will not take the browser to a new URL
  
          event.stopPropagation();
          makeHeaderInactive(header.getElement());
      }
docs: Needed for header widgets to prevent expand/collapse on their clicks.