designMode-on-of-lazy-loading-iframe.html

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<style>
*::first-letter {}
</style>
<script>
addEventListener("load", () => {
  const iframe = document.querySelector("iframe");
  iframe.contentWindow.focus();
  document.styleSheets[0].deleteRule(0);
  iframe.contentWindow.document.designMode = "on";
});
</script>
</head>
<body>
<iframe loading="lazy">
</body>
</html>

chromium/third_party/blink/web_tests/external/wpt/editing/crashtests/designMode-on-of-lazy-loading-iframe.html