code: protected void renderHeaderCellContents(AbstractRenderAppender appender, String jspFragmentOutput)
              throws IOException, JspException {
  
          if(_headerValue == null) {
              appender.append(jspFragmentOutput);
          }
          else {
              _headerCellModel.setDataGridTagModel(DataGridUtil.getDataGridTagModel(getJspContext()));
                  _headerCellModel.setBodyContent(jspFragmentOutput);
              _headerCellModel.setValue(_headerValue);
  
              getCellDecorator().decorate(getJspContext(), appender, _headerCellModel);
          }
      }
docs: Render the contents of the body of the HTML th tag into the given {@link AbstractRenderAppender}
  @param appender the {@link AbstractRenderAppender} for the output
  @param jspFragmentOutput the result of having evaluated the tag's {@link JspFragment}
  @throws IOException when an error occurs writing to the output stream
  @throws JspException when an error occurs evaluating the {@link JspFragment} for this body