<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <meta http-equiv="Content-Security-Policy" content="frame-src 'self'">
  <script>
    // The following is the content of a srcdoc iframe. It contains:
    // - a script that catches the frame-src securitypolicyviolation event and
    // forwards the information to the parent,
    // - a cross-origin iframe.
    let doc = `
      <script>
        window.addEventListener("securitypolicyviolation", e => {
          if (e.violatedDirective === "frame-src") {
            window.top.postMessage("frame blocked", "*");
          }
        });
      </scr` + `ipt>
      <iframe src="http://{{hosts[alt][]}}:{{ports[http][0]}}/content-security-policy/inheritance/support/postmessage-top.html"></iframe>`;
    doc = doc.replaceAll('"', "\\\'");

    const js_url = "javascript:'<iframe srcdoc=\""+ doc +"\">'";
    window.open(js_url, "_self");
  </script>
</head>
