CustomRenderMatcher supMatcher() =>
    (context) => context.tree.element?.localName == 'sup';

Html(
  data: snapshot.data?[widget.cmsKey],
  style: btmHctHtmlStyle(),
  customRenders: {
    supMatcher(): CustomRender.widget(
      widget: (con, buildChildren) => ReferenceBox(
          text: con.tree.element!.innerHtml,
          linked: true,
          leftMargin: 4.0),
    ),
  },
  onLinkTap: (String? url, RenderContext rc,
      Map<String, String> attributes, element) async {
    onLinkTap(context, url, rc, attributes, element);
  },
),