code: @Override
      public void setText(String text) {
          if (text == null) {
              if (headerElem != null) {
                  removeChild(headerElem);
                  headerElem = null;
              }
              return;
          }
  
          if (headerElem == null) {
              headerElem = Document.get().createHElement(3);
              attachChild(headerElem);
          }
          headerElem.setInnerText(text);
      }
docs: Sets the content of the "main" text to the given value.