third_party/blink/web_tests/shadow-dom/slots-dynamic.html - manifest_repos/chromium_src - Git at Google

 <!DOCTYPE html>
 <div id='host'>
   <div slot='s1'>c1</div>
   <div slot='s2'>c2</div>
 </div>
 <script>
 'use strict';
 const slot = document.createElement('slot');
 slot.setAttribute('name', 's1');
 host.attachShadow({mode: 'open'}).appendChild(slot);
 </script>
	<!DOCTYPE html>
	<div id='host'>
	<div slot='s1'>c1</div>
	<div slot='s2'>c2</div>
	</div>
	<script>
	'use strict';
	const slot = document.createElement('slot');
	slot.setAttribute('name', 's1');
	host.attachShadow({mode: 'open'}).appendChild(slot);
	</script>