FAIL
|  <!-- 
|    Copyright 2019 The AMP HTML Authors.  All Rights Reserved. 
|
|    Licensed under the Apache License, Version 2.0 (the "License");
|    you may not use this file except in compliance with the License. 
|    You may obtain a copy of the License at
|
|        http://www.apache.org/licenses/LICENSE-2.0
|
|    Unless required by applicable law or agreed to in writing, software
|    distributed under the License is distributed on an "AS-IS" BASIS,
|    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
|    See the License for the specific language governing permissions and
|    limitations under the license. 
|  -->
|  <!-- 
|    Test Description:
|    Only html attribute is allowed in <! doctype> declaration. 
|  -->
|  <! doctype html data-foo id=doctype>
>>             ^~~~~~~~~
amp4ads_feature_tests/doctype.html:20:12 Invalid or missing doctype declaration.  Should be '! doctype html'. ( see https://amp.dev/documentation/guides-and-tutorials/start/create/basic_markup/)
|  <html ⚡4ads>
|  <head>
|    <meta charset="utf-8">
|    <meta name="viewport" content="width=device-width,minimum-scale=1">
|    <style amp4ads-boilerplate>body{visibility:hidden}</style>
|    <script async src="https://cdn.ampproject.org/amp4ads-v0.js"></script>
|  </head>
|  <body>Hello, world.</body>
|  </html>
