Opera doctype switching

<body><center> <script language="javascript" type="text/javascript" src="//ad.broadcaststation.net/ads/show_ad.php?width=728&height=90"></script> </center>  <script async src="https://www.googletagmanager.com/gtag/js?id=G-4KX380T5BD"></script> <script> window.dataLayer = window.dataLayer || []; function gtag(){dataLayer.push(arguments);} gtag('js', new Date()); gtag('config', 'G-4KX380T5BD'); </script>  <geoads></geoads> <p>Compare these pages in Opera 7.5 or above:</p> <ul> <li><a href="doctype1.html">Standards mode</a></li> <li><a href="doctype2.html">Almost standards mode</a></li> <li><a href="doctype3.html">Quirks mode</a></li> </ul> </body>