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chromium/third_party/blink/web_tests/external/wpt/html/semantics/forms/form-submission-target/rel-base-target.html 

<!DOCTYPE html>
<title>&lt;form rel> with &lt;base target></title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src=resources/reltester.js></script>
<base target=_blank>
<div id=log></div>
<form action=resources/endpoint.html><input type=hidden name=channelname></form>
<script>
const submitter = document.querySelector("form"),
      channelInput = document.querySelector("input");
relTester(submitter, channelInput, "<base target>");
</script>