code: public void setOpen(boolean open) {
  
          m_opened = open;
          if (m_opened) {
              // show content
              m_visibilityStyle.setValue(
                  I_CmsLayoutBundle.INSTANCE.generalCss().cornerAll()
                      + " "
                      + I_CmsLayoutBundle.INSTANCE.fieldsetCss().fieldsetVisible());
              m_opener.setDown(true);
          } else {
              // hide content
              m_visibilityStyle.setValue(I_CmsLayoutBundle.INSTANCE.fieldsetCss().fieldsetInvisible());
              m_opener.setDown(false);
          }
          CmsDomUtil.resizeAncestor(getParent());
      }
docs: Sets the fieldset open, showing the content.<p>
  
  @param open <code>true</code> to open the fieldset