initial attempt

extensions/amp-mustache/0.2/amp-mustache.js

@@ -145,7 +145,68 @@ export class AmpMustache extends BaseTemplate {
   purifyAndSetHtml_(html) {
     const body = this.purifier_.purifyHtml(`<div>${html}</div>`);
     const div = body.firstElementChild;
-    return this.tryUnwrap(div);
+    return tryUnwrap(div);
+  }
+
+  /**
+   * Iterate through the child nodes of the given root, applying the
+   * given callback to non-empty text nodes and elements.
+   * @param {!Element} root
+   * @param {function((!Element|string))} callback
+   */
+  visitChildren_(root, callback) {
+    for (let n = root.firstChild; n != null; n = n.nextSibling) {
+      if (n.nodeType == /* TEXT */ 3) {
+        const text = n.textContent.trim();
+        if (text) {
+          callback(text);
+        }
+      } else if (n.nodeType == /* COMMENT */ 8) {
+        // Ignore comments.
+      } else if (n.nodeType == /* ELEMENT */ 1) {
+        callback(dev().assertElement(n));
+      }
+    }
+  }
+
+  /**
+   * Unwraps the root element and returns any children in an array.
+   * Text node children are normalized inside a <div>.
+   * @param {!Element} root
+   * @return {!Array<!Element>}
+   * @protected @final
+   */
+  unwrapChildren(root) {
+    const children = [];
+    visitChildren_(root, (c) => {
+      if (typeof c == 'string') {
+        const element = this.win.document.createElement('div');
+        element.textContent = c;
+        children.push(element);
+      } else {
+        children.push(c);
+      }
+    });
+    return children;
+  }
+
+  /**
+   * Unwraps the root element. If root has a single element child,
+   * returns the child. Otherwise, returns root.
+   * @param {!Element} root
+   * @return {!Element}
+   * @protected @final
+   */
+  tryUnwrap(root) {
+    let onlyChild;
+    visitChildren_(root, (c) => {
+      if (onlyChild === undefined && c.nodeType) {
+        onlyChild = c;
+      } else {
+        onlyChild = null;
+      }
+    });
+    return onlyChild || root;
   }
 }