Verify in tests that alt="" does not contain element type.

app/lib/frontend/dom/dom.dart

@@ -448,6 +448,8 @@ class Image {
 
   Image({
     required this.src,
+
+    /// Note: the `alt` text of elements should not include the element type (e.g. `icon`).
     required this.alt,
     required this.width,
     required this.height,

pkg/_pub_shared/lib/validation/html/html_validation.dart

@@ -29,38 +29,37 @@ void parseAndValidateHtml(String html) {
 /// - `<script> tags have no `src` attribute or have content (except `ld+json`
 ///   meta content).
 void validateHtml(Node root) {
-  List<Element> elements;
-  List<Element> links;
-  List<Element> scripts;
-  List<Element> buttons;
-
+  late List<Element> Function(String selector) querySelectorAll;
   if (root is DocumentFragment) {
-    elements = root.querySelectorAll('*');
-    links = root.querySelectorAll('a');
-    scripts = root.querySelectorAll('script');
-    buttons = root.querySelectorAll('button');
+    querySelectorAll = root.querySelectorAll;
   } else if (root is Document) {
     _validateCanonicalLink(root.querySelector('head')!);
-    elements = root.querySelectorAll('*');
-    links = root.querySelectorAll('a');
-    scripts = root.querySelectorAll('script');
-    buttons = root.querySelectorAll('button');
+    querySelectorAll = root.querySelectorAll;
   } else {
     throw AssertionError('Unknown html element type: $root');
   }
 
-  // No inline JS attribute
-  for (Element elem in elements) {
+  for (final elem in querySelectorAll('*')) {
+    // No inline JS attribute
     for (final attr in elem.attributes.keys) {
       final name = attr.toString();
       if (name.toLowerCase().startsWith('on')) {
         throw AssertionError(
             'No inline JS attribute is allowed, found: ${elem.outerHtml}.');
       }
     }
+    // alt attribute should not contain the element type
+    final alt = elem.attributes['alt']?.toLowerCase();
+    if (alt != null) {
+      if (alt.split(' ').contains('icon')) {
+        throw AssertionError(
+            '"alt" attribute should not contain the type of the elemnt: ${elem.outerHtml}');
+      }
+    }
   }
 
   // All <a target="_blank"> links must have rel="noopener"
+  final links = querySelectorAll('a');
   for (Element elem in links) {
     if (elem.attributes['target'] == '_blank') {
       if (!elem.attributes.containsKey('rel')) {
@@ -97,6 +96,7 @@ void validateHtml(Node root) {
   }
 
   // No inline script tag.
+  final scripts = querySelectorAll('script');
   for (Element elem in scripts) {
     if (elem.attributes['type'] == 'application/ld+json') {
       if (elem.attributes.length != 1) {
@@ -130,6 +130,7 @@ void validateHtml(Node root) {
   }
 
   // Lighthouse flags buttons that don't have text content or an `aria-label` property.
+  final buttons = querySelectorAll('button');
   for (final elem in buttons) {
     final text = elem.attributes['aria-label']?.trim() ?? elem.text.trim();
     if (text.isEmpty) {