chromium/third_party/blink/web_tests/external/wpt/html/webappapis/user-prompts/newline-normalization-manual.html

<!DOCTYPE html>
<meta charset="utf-8">
<title>Newline normalization in simple dialogs</title>
<link rel="help" href="https://html.spec.whatwg.org/multipage/#simple-dialogs">

<p>The dialogs should all contain text looking like:</p>

<pre>Line 1.1
Line 1.2
Line 1.3
Line 1.4

Line 2.1</pre>

<script>
"use strict";

for (const func of [alert, confirm, prompt]) {
  func('Line 1.1\nLine 1.2\rLine 1.3\r\nLine 1.4\n\rLine 2.1');
}
</script>