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chromium/third_party/blink/web_tests/editing/selection/set_base_and_extent/set_null.html 

<!doctype html>
<script src="../../../resources/testharness.js"></script>
<script src="../../../resources/testharnessreport.js"></script>
<script src="../../assert_selection.js"></script>
<div id="log"></div>
<script>
test(() => {
assert_selection(
  '<div>^foo|</div>',
  selection => {
    selection.setBaseAndExtent(null, 0, null, 0);
  },
  '<div>foo</div>',
  'Setting both null clears selection');

assert_selection(
  '<div>^foo|</div>',
  selection => {
    selection.setBaseAndExtent(null, 1, null, 2);
  },
  '<div>foo</div>',
  'Setting both null clears selection');

assert_selection(
  '<div>^foo|</div>',
  selection => selection.setBaseAndExtent(null, 1, selection.document.querySelector('div'), 1),
  '<div>foo</div>',
  'Setting only base null clears selection');

assert_selection(
  '<div>foo</div>',
  selection => selection.setBaseAndExtent(selection.document.querySelector('div'), 0, null, 2),
  '<div>|foo</div>',
  'Setting base non-null and extent null behaves as collapse.' +
  'This is under discussion: https://github.com/w3c/selection-api/issues/72');

}, 'setBaseAndExtent with null.');
</script>