chromium/third_party/blink/web_tests/external/wpt/css/css-view-transitions/paint-holding-in-iframe-ref.html

<!DOCTYPE html>
<html>
<title>View transitions: display old paint during update callback (ref)</title>
<link rel="help" href="https://drafts.csswg.org/css-view-transitions-1/">
<link rel="author" href="mailto:[email protected]">
<style>
  .new {
    border: 5px solid orange;
  }
</style>

<iframe id="inner" class="new" srcdoc="
  <style>
    body {
      background: blue;
    }
  </style>
  <body>
    This is old content
  </body>
"></iframe>
</html>