Refactor Thead Th scope Markdown plugin (#37299)

lib/render-content/plugins/rewrite-thead-th-scope.js

@@ -0,0 +1,35 @@
+import { visitParents } from 'unist-util-visit-parents'
+
+/**
+ * Where it can mutate the AST to swap from:
+ *
+ *   <thead>
+ *     <tr>
+ *       <th>...</th>
+ *       <th>...</th>
+ *
+ * to:
+ *   <thead>
+ *     <tr>
+ *       <th scope="col">...</th>
+ *       <th scope="col">...</th>
+ *
+ * */
+
+function matcher(node) {
+  return node.type === 'element' && node.tagName === 'th' && !('scope' in node.properties)
+}
+
+function visitor(node, ancestors) {
+  const parent = ancestors.at(-1)
+  if (parent && parent.tagName === 'tr') {
+    const grandParent = ancestors.at(-2)
+    if (grandParent && grandParent.tagName === 'thead') {
+      node.properties.scope = 'col'
+    }
+  }
+}
+
+export default function rewriteTheadThScope() {
+  return (tree) => visitParents(tree, matcher, visitor)
+}