diff --git a/source b/source
index eb7730afdb1..96bdd896f83 100644
--- a/source
+++ b/source
@@ -82005,9 +82005,18 @@ popup4.close();</code></pre></div>
    otherwise <var>embedder</var>'s <span>relevant settings object</span>'s <span>top-level
    origin</span>.</p></li>
 
+   <li><p>Let <var>crossSiteAncestorFlag</var> be false if <var>embedder</var> is null; otherwise
+   <var>embedder</var>'s <span data-x="concept-environment-cross-site-ancestor">cross-site ancestor
+   flag</span>.</p></li>
+
+   <li><p>If <var>crossSiteAncestorFlag</var> is false, <var>embedder</var> is not null, and
+   <var>origin</var> is not <span>same site</span> with <var>embedder</var>'s <span
+   data-x="concept-settings-object-origin">origin</span>, then set <var>crossSiteAncestorFlag</var>
+   to true.</p></li>
+
    <li><p><span>Set up a window environment settings object</span> with <code>about:blank</code>,
-   <var>realm execution context</var>, null, <var>topLevelCreationURL</var>, and
-   <var>topLevelOrigin</var>.</p></li>
+   <var>realm execution context</var>, null, <var>topLevelCreationURL</var>,
+   <var>topLevelOrigin</var>, and <var>crossSiteAncestorFlag</var>.</p></li>
 
    <li><p>Let <var>loadTimingInfo</var> be a new <span>document load timing info</span> with
    its <span>navigation start time</span> set to the result of calling <span>coarsen time</span>
@@ -84300,8 +84309,8 @@ interface <dfn interface>BarProp</dfn> {
   <p>To <dfn>set up a window environment settings object</dfn>, given a <span>URL</span>
   <var>creationURL</var>, a <span>JavaScript execution context</span> <var>execution context</var>,
   null or an <span>environment</span> <var>reservedEnvironment</var>, a <span>URL</span>
-  <var>topLevelCreationURL</var>, and an <span>origin</span> <var>topLevelOrigin</var>, run these
-  steps:</p>
+  <var>topLevelCreationURL</var>, an <span>origin</span> <var>topLevelOrigin</var>, and a boolean
+  <var>crossSiteAncestorFlag</var>, run these steps:</p>
 
   <ol>
    <li><p>Let <var>realm</var> be the value of <var>execution context</var>'s Realm
@@ -84410,8 +84419,10 @@ interface <dfn interface>BarProp</dfn> {
 
    <li><p>Set <var>settings object</var>'s <span data-x="concept-environment-creation-url">creation
    URL</span> to <var>creationURL</var>, <var>settings object</var>'s <span>top-level creation
-   URL</span> to <var>topLevelCreationURL</var>, and <var>settings object</var>'s <span>top-level
-   origin</span> to <var>topLevelOrigin</var>.</p></li>
+   URL</span> to <var>topLevelCreationURL</var>, <var>settings object</var>'s <span>top-level
+   origin</span> to <var>topLevelOrigin</var>, and <var>settings object</var>'s <span
+   data-x="concept-environment-cross-site-ancestor">cross-site ancestor flag</span> to
+   <var>crossSiteAncestorFlag</var>.</p></li>
 
    <li><p>Set <var>realm</var>'s [[HostDefined]] field to <var>settings object</var>.</p></li>
   </ol>
@@ -89817,6 +89828,8 @@ interface <dfn interface>Location</dfn> { // but see also <a href="#the-location
 
        <li><p>Let <var>topLevelOrigin</var> be null.</p></li>
 
+       <li><p>Let <var>crossSiteAncestorFlag</var> be false.</p></li>
+
        <li>
         <p>If <var>browsingContext</var> is not a <span>top-level browsing context</span>, then:</p>
 
@@ -89827,6 +89840,14 @@ interface <dfn interface>Location</dfn> { // but see also <a href="#the-location
          <li><p>Set <var>topLevelCreationURL</var> to <var>parentEnvironment</var>'s <span>top-level
          creation URL</span> and <var>topLevelOrigin</var> to <var>parentEnvironment</var>'s
          <span>top-level origin</span>.</p></li>
+
+         <li><p>Set <var>crossSiteAncestorFlag</var> to <var>parentEnvironment</var>'s <span
+         data-x="concept-environment-cross-site-ancestor">cross-site ancestor flag</span>.</p></li>
+
+         <li><p>If <var>crossSiteAncestorFlag</var> is false and <var>parentEnvironment</var>'s
+         <span data-x="concept-settings-object-origin">origin</span> is not <span>same site</span>
+         with <var>currentURL</var>'s <span data-x="concept-url-origin">origin</span>, then set
+         <var>crossSiteAncestorFlag</var> to true.
         </ol>
        </li>
 
@@ -89837,8 +89858,9 @@ interface <dfn interface>Location</dfn> { // but see also <a href="#the-location
         data-x="concept-environment-target-browsing-context">target browsing context</span> is
         <var>browsingContext</var>, <span data-x="concept-environment-creation-url">creation
         URL</span> is <var>currentURL</var>, <span>top-level creation URL</span> is
-        <var>topLevelCreationURL</var>, and <span>top-level origin</span> is
-        <var>topLevelOrigin</var>.</p>
+        <var>topLevelCreationURL</var>, <span>top-level origin</span> is
+        <var>topLevelOrigin</var>, and <span data-x="concept-environment-cross-site-ancestor">
+        cross-site ancestor flag</span> is <var>crossSiteAncestorFlag</var>.</p>
 
         <p class="note">The created environment's <span
         data-x="concept-environment-active-service-worker">active service worker</span> is set in
@@ -90462,6 +90484,8 @@ interface <dfn interface>Location</dfn> { // but see also <a href="#the-location
      <li><p>Let <var>topLevelOrigin</var> be <var>navigationParams</var>'s <span
      data-x="navigation-params-request">origin</span>.</p></li>
 
+     <li><p>Let <var>crossSiteAncestorFlag</var> be false.</p></li>
+
      <li>
       <p>If <var>browsingContext</var> is not a <span>top-level browsing context</span>, then:</p>
 
@@ -90474,13 +90498,22 @@ interface <dfn interface>Location</dfn> { // but see also <a href="#the-location
 
        <li><p>Set <var>topLevelOrigin</var> to <var>parentEnvironment</var>'s <span>top-level
        origin</span>.</p></li>
+
+       <li><p>Set <var>crossSiteAncestorFlag</var> to <var>parentEnvironment</var>'s <span
+       data-x="concept-environment-cross-site-ancestor">cross-site ancestor flag</span>.</p></li>
+
+       <li><p>If <var>crossSiteAncestorFlag</var> is false and <var>navigationParams</var>'s <span
+       data-x="navigation-params-request">origin</span> is not <span>same site</span> with
+       <var>parentEnvironment</var>'s <span data-x="concept-settings-object-origin">origin</span>,
+       then set <var>crossSiteAncestorFlag</var> to true.</p>
       </ol>
      </li>
 
      <li><p><span>Set up a window environment settings object</span> with <var>creationURL</var>,
      <var>realm execution context</var>, <var>navigationParams</var>'s <span
      data-x="navigation-params-reserved-environment">reserved environment</span>,
-     <var>topLevelCreationURL</var>, and <var>topLevelOrigin</var>.</p></li>
+     <var>topLevelCreationURL</var>, <var>topLevelOrigin</var>, and
+     <var>crossSiteAncestorFlag</var>.</p></li>
     </ol>
 
     <p class="note">This is the usual case, where the new <code>Document</code> we're about to
@@ -92834,6 +92867,15 @@ interface <dfn interface>BeforeUnloadEvent</dfn> : <span>Event</span> {
     involved.</p>
    </dd>
 
+   <dt>A <dfn data-x="concept-environment-cross-site-ancestor" export for="environment">cross-site
+   ancestor flag</dfn></dt>
+   <dd><p>A boolean. For window <span>environment settings object</span>s this will be set to true
+   if an ancestor frame has an <span data-x="concept-settings-object-origin">origin</span> that is
+   not <span>same site</span> with the current window's <span
+   data-x="concept-settings-object-origin">origin</span> and otherwise false.  For workers and
+   worklets it is set to the <span data-x="concept-environment-cross-site-ancestor">cross-site
+   ancestor flag</span> of its creator.</p></dd>
+
    <dt>A <dfn data-x="concept-environment-target-browsing-context" export
    for="environment">target browsing context</dfn></dt>
    <dd><p>Null or a target <span>browsing context</span> for a <span
@@ -105005,8 +105047,10 @@ interface <dfn interface>SharedWorkerGlobalScope</dfn> : <span>WorkerGlobalScope
    unique opaque string, <span data-x="concept-environment-creation-url">creation URL</span> to
    <var>worker global scope</var>'s <span>url</span>, <span>top-level creation URL</span> to null,
    <span data-x="concept-environment-target-browsing-context">target browsing context</span> to
-   null, and <span data-x="concept-environment-active-service-worker">active service worker</span>
-   to null.</p></li>
+   null, <span data-x="concept-environment-active-service-worker">active service worker</span>
+   to null, and <span data-x="concept-environment-cross-site-ancestor">cross-site ancestor flag
+   </span> to <var>outside settings</var>'s <span data-x="concept-environment-cross-site-ancestor">
+   cross-site ancestor flag</span>.</p></li>
 
    <li><p>If <var>worker global scope</var> is a <code>DedicatedWorkerGlobalScope</code> object,
    then set <var>settings object</var>'s <span>top-level origin</span> to <var>outside