Issue #3468538 by mably, SirClickalot: Flexibility in targeting heading tags

Closes #3468538

js/toc_js.js

@@ -3,14 +3,19 @@
  * Toc.js.
  */
 (($, once) => {
+  function decodeHtml(html) {
+    const textarea = document.createElement('textarea');
+    textarea.innerHTML = html;
+    return textarea.value;
+  }
   Drupal.behaviors.toc_js = {
     attach(context, settings) {
       once('toc_js', '.toc-js', context).forEach((elt) => {
         const $tocEl = $(elt);
         const options = {
           listType: $tocEl.data('list-type') === 'ol' ? 'ol' : 'ul',
-          selectors: $tocEl.data('selectors') || 'h2, h3',
-          container: $tocEl.data('container') || 'body',
+          selectors: decodeHtml($tocEl.data('selectors')) || 'h2, h3',
+          container: decodeHtml($tocEl.data('container')) || 'body',
           selectorsMinimum: $tocEl.data('selectors-minimum') || 0,
           stickyOffset: $tocEl.data('sticky-offset') || 0,
           prefix: $tocEl.data('prefix') || '',