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chromium/third_party/blink/web_tests/external/wpt/selection/caret/collapse-pre-linestart-ref.html 

<!DOCTYPE html>
<meta charset="utf-8">
<title>selection.collapse() to line start</title>
<pre id=target contenteditable>ABC<br><br></pre>
<script>
  target.focus();
  getSelection().collapse(target, 3);
</script>