third_party/blink/web_tests/shadow-dom/imperative-apis/test-custom-detail-summary.html - chromium/src - Git at Google

 <!DOCTYPE html>
 <script src="custom-detail-summary.js"></script>

 <my-detail id="my-detail">
   <p>another test</p>
   <my-summary id="my-summary">summary</my-summary>
 </my-detail>
 <my-summary id="my-summary1">added-summary</my-summary>
 <script>
 const host = document.querySelector("#my-detail");
 const sum = document.querySelector("#my-summary");
 const sum1 = document.querySelector("#my-summary1");
 host.insertBefore(sum1, sum);
 </script>
	<!DOCTYPE html>
	<script src="custom-detail-summary.js"></script>

	<my-detail id="my-detail">
	<p>another test</p>
	<my-summary id="my-summary">summary</my-summary>
	</my-detail>
	<my-summary id="my-summary1">added-summary</my-summary>
	<script>
	const host = document.querySelector("#my-detail");
	const sum = document.querySelector("#my-summary");
	const sum1 = document.querySelector("#my-summary1");
	host.insertBefore(sum1, sum);
	</script>