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diff --git a/testing/web-platform/tests/html/semantics/popovers/popover-anchor-scroll-display.tentative.html b/testing/web-platform/tests/html/semantics/popovers/popover-anchor-scroll-display.tentative.html
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+<!DOCTYPE html>
+<html class="reftest-wait">
+<meta charset="utf-8">
+<link rel=author href="mailto:xiaochengh@chromium.org">
+<link rel=help href="https://open-ui.org/components/popover.research.explainer">
+<link rel=help href="https://html.spec.whatwg.org/multipage/popover.html">
+<link rel=match href="popover-anchor-scroll-display-ref.html">
+
+<div class=spacer style="height: 200px"></div>
+
+<p>There should be a green box attached to the right side of each orange box.</p>
+
+<!-- Example using the `anchor` implicit reference element -->
+<div class=ex>
+  <div class=anchor id=anchor1></div>
+  <div id=popover1 popover=manual anchor=anchor1></div>
+</div>
+
+<!-- Example using a default anchor that is not the implicit anchor -->
+<div class=ex>
+  <div class=anchor id=anchor2></div>
+  <div id=popover2 popover=manual anchor=fake-anchor></div>
+</div>
+
+<!-- A position:fixed fake anchor. Any popover anchored to it won't move when
+     the document is scrolled. -->
+<div id=fake-anchor></div>
+
+<div class=spacer style="height: 200vh"></div>
+
+<style>
+  .ex {
+    margin: 25px;
+  }
+  .ex div {
+    width: 100px;
+    height: 100px;
+  }
+  .anchor {
+    background: orange;
+  }
+  [popover] {
+    background: lime;
+    padding:0;
+    border:0;
+  }
+  #popover1 {
+    left: anchor(right);
+    top: anchor(top);
+  }
+  #fake-anchor {
+    position: fixed;
+    anchor-name: --fake-anchor;
+  }
+  #anchor2 {
+    anchor-name: --anchor2;
+  }
+  #popover2 {
+    anchor-default: --anchor2;
+    left: anchor(right);
+    top: anchor(top);
+  }
+</style>
+
+<script>
+function raf() {
+  return new Promise(resolve => requestAnimationFrame(resolve));
+}
+
+async function runTest() {
+  document.querySelectorAll('[popover]').forEach(
+      popover => popover.showPopover());
+
+  // Render a frame at the intial scroll position.
+  await raf();
+  await raf();
+
+  document.documentElement.scrollTop = 100;
+  document.documentElement.classList.remove('reftest-wait');
+
+  // The popover should still be attached to the anchor.
+}
+runTest();
+</script>
+
+</html>