diff --git a/inst/reveal.js-5.2.1/dist/theme/ids.css b/inst/reveal.js-5.2.1/dist/theme/ids.css
index 5ae8600..16c8f5e 100644
--- a/inst/reveal.js-5.2.1/dist/theme/ids.css
+++ b/inst/reveal.js-5.2.1/dist/theme/ids.css
@@ -1074,6 +1074,13 @@
   padding: 0 0 0 1.1em;
   font-weight: normal;
 }
+.reveal .ids-overview-toc.with-subheadings {
+  columns: 2;
+  column-gap: 2.5em;
+}
+.reveal .ids-overview-toc.with-subheadings > li {
+  break-inside: avoid;
+}
 .reveal .ids-overview-toc ul li {
   margin: 0.18em 0;
 }
diff --git a/inst/rmarkdown/templates/revealjs_presentation/resources/default.html b/inst/rmarkdown/templates/revealjs_presentation/resources/default.html
index a557cf6..9bda0eb 100644
--- a/inst/rmarkdown/templates/revealjs_presentation/resources/default.html
+++ b/inst/rmarkdown/templates/revealjs_presentation/resources/default.html
@@ -978,9 +978,11 @@
 $endif$
 <script>
   // Slides whose (only) heading is "Overview" or "Überblick" are
-  // automatically populated with a table of contents built from the deck's
-  // h1/h2 slide headings, replacing whatever body content the slide had
-  // (ported from the Google Docs slide workflow). Styling in the ids theme.
+  // automatically populated with a table of contents of the deck's h1 slide
+  // headings, replacing whatever body content the slide had (ported from the
+  // Google Docs slide workflow). By adding {data-overview-subheadings=true}
+  // to the heading, h2 sub-headings are included below their chapters and
+  // the list is laid out in two columns. Styling in the ids theme.
   (function () {
     var TITLES = ['overview', 'überblick'];
 
@@ -998,13 +1000,17 @@
         if (!isOverviewSlide(target) || target.dataset.tocDone) return;
         target.dataset.tocDone = '1';
         var heading = target.querySelector('h1,h2');
+        var includeSub = (heading.getAttribute('data-overview-subheadings') || '')
+          .toLowerCase() !== 'false'
+          && heading.hasAttribute('data-overview-subheadings');
         var list = document.createElement('ul');
         list.className = 'ids-overview-toc';
+        if (includeSub) list.classList.add('with-subheadings');
         var subList = null;
         slides.forEach(function (slide) {
           if (slide === target || !slide.id || isOverviewSlide(slide)) return;
           var h = slide.querySelector('h1,h2');
-          if (!h) return;
+          if (!h || (h.tagName !== 'H1' && !includeSub)) return;
           var link = document.createElement('a');
           link.href = '#/' + slide.id;
           link.textContent = h.textContent;