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chromium/third_party/blink/web_tests/external/wpt/html/semantics/forms/textfieldselection/setSelectionRange.html 

<!doctype html>
<meta charset="utf-8">
<title></title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<textarea>

</textarea>
<script>
test(function() {
    let textarea = document.querySelector('textarea');
    assert_equals(textarea.selectionStart, 0);
    assert_equals(textarea.selectionEnd, 0);
    textarea.setSelectionRange(0, 1);
    assert_equals(textarea.selectionStart, 0);
    assert_equals(textarea.selectionEnd, 1);
}, "setSelectionRange on line boundaries");
</script>