diff --git a/source b/source
index f454a1fd8a8..b7d12fbc127 100644
--- a/source
+++ b/source
@@ -2855,6 +2855,8 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
 
     <ul class="brief">
      <li><dfn data-x-href="https://tc39.github.io/ecma262/#active-function-object">active function object</dfn></li>
+     <li><dfn data-x-href="https://tc39.github.io/ecma262/#sec-agents">agent</dfn> and
+         <dfn data-x-href="https://tc39.github.io/ecma262/#sec-agent-clusters">agent cluster</dfn></li>
      <li><dfn data-x-href="https://tc39.github.io/ecma262/#sec-automatic-semicolon-insertion">automatic semicolon insertion</dfn></li>
      <li>The <dfn data-x-href="https://tc39.github.io/ecma262/#current-realm">current Realm Record</dfn></li>
      <li><dfn data-x-href="https://tc39.github.io/ecma262/#early-error-rule">early error</dfn></li>
@@ -2936,6 +2938,7 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
      <li>The <dfn data-x="js-abstract-equality" data-x-href="https://tc39.github.io/ecma262/#sec-abstract-equality-comparison">Abstract Equality Comparison</dfn> algorithm</li>
      <li>The <dfn data-x="js-strict-equality" data-x-href="https://tc39.github.io/ecma262/#sec-strict-equality-comparison">Strict Equality Comparison</dfn> algorithm</li>
      <li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-date-objects"><code>Date</code></dfn> class</li>
+     <li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-sharedarraybuffer-objects"><code>SharedArrayBuffer</code></dfn> class</li>
      <li>The <dfn data-x-href="https://tc39.github.io/ecma262/#sec-native-error-types-used-in-this-standard-typeerror"><code>TypeError</code></dfn> class</li>
      <li>The <dfn data-x="js-RangeError" data-x-href="https://tc39.github.io/ecma262/#sec-native-error-types-used-in-this-standard-rangeerror"><code>RangeError</code></dfn> class</li>
      <li>The <dfn data-x="js-typeof" data-x-href="https://tc39.github.io/ecma262/#sec-typeof-operator"><code>typeof</code></dfn> operator</li>
@@ -88419,6 +88422,101 @@ import "https://example.com/foo/../module2.js";</pre>
    data-x="concept-module-script-module-record">module record</span>.</p></li>
   </ol>
 
+  <h5>Integration with the JavaScript agent formalism</h5>
+
+  <p>JavaScript defines the concept of an <span>agent</span>. This corresponds, in a 1-to-1 manner,
+  with this specification's concept of an <span>environment settings object</span>.</p>
+
+  <p class="warning">See also <a href="https://github.com/tc39/ecma262/issues/882">tc39/ecma262
+  issue #882</a>.</p>
+
+  <p>To determine the manifestation of JavaScript's <span>agent cluster</span> concept in user
+  agents, we first define the set of <dfn>directly-shared environment settings objects</dfn> for a
+  given <span>environment settings object</span> <var>settingsObject</var>:</p>
+
+  <dl class="switch">
+   <dt>For a <var>settingsObject</var> with a <span>responsible document</span></dt>
+   <dd>
+    <p>The set containing:</p>
+
+    <ul>
+     <li><var>settingsObject</var>,</li>
+     <li>any <span>environment settings object</span> whose <span>responsible browsing
+     context</span> is in the same <span>unit of related similar-origin browsing contexts</span> as
+     <var>settingsObject</var>'s <span>responsible browsing context</span>,</li>
+     <li>and any <span>environment settings object</span> whose <span
+     data-x="concept-settings-object-global">global object</span> is a
+     <code>DedicatedWorkerGlobalScope</code> object of which <span>the worker's owners</span>
+     contains <var>settingsObject</var>'s <span>responsible document</span>.</li>
+    </ul>
+   </dd>
+
+   <dt>For a <var>settingsObject</var> whose <span data-x="concept-settings-object-global">global
+   object</span> is a <code>DedicatedWorkerGlobalScope</code> object</dt>
+   <dd>
+    <p>The set containing:
+
+    <ul>
+     <li><var>settingsObject</var>,</li>
+     <li>the <span>relevant settings object</span> of <var>settingsObject</var>'s
+     <span data-x="concept-settings-object-global">global object</span>'s single <span data-x="the
+     worker's owners">the worker's owner</span>,</li>
+     <li>any <span>relevant settings object</span> of <var>settingsObject</var>'s
+     <span data-x="concept-settings-object-global">global object</span>'s <span>the worker's
+     workers</span> that are not <code>SharedWorkerGlobalScope</code> objects.</li>
+    </ul>
+   </dd>
+
+   <dt>Otherwise (a shared or service worker)</dt>
+   <dd><p>The set containing <var>settingsObject</var> and any <span>relevant settings object</span>
+   of <var>settingsObject</var>'s <span data-x="concept-settings-object-global">global
+   object</span>'s <span>the worker's workers</span> that are not
+   <code>SharedWorkerGlobalScope</code> objects.</p>
+  </dl>
+
+  <p class="warning">What to do with worklets?</p>
+
+  <p>Then, the transitive closure of all <span data-x="environment settings object">environment
+  settings objects</span> that are <span>directly-shared environment settings objects</span> are the
+  <dfn>shared environment settings objects</dfn>, and a JavaScript <span>agent cluster</span>
+  consists of all the corresponding <span data-x="agent">agents</span>.</p>
+
+  <p class="note">The <span>agent cluster</span> concept is crucial for defining the JavaScript
+  memory model, and in particular among which <span data-x="agent">agents</span> the backing data of
+  <code>SharedArrayBuffer</code> objects can be shared.</p>
+
+  <div class="example">
+   <p>The following pairs of global objects are each within the same <span>shared environment
+   settings objects</span>, and thus can use <code>SharedArrayBuffer</code> instances to share
+   memory with each other:</p>
+
+   <ul class="brief">
+    <li>A <code>Window</code> and a dedicated worker that it created</li>
+
+    <li>A worker (of any type) and a dedicated worker it creates</li>
+
+    <li>A <code>Window</code> and the <code>Window</code> of an <code>iframe</code> element that
+    could be <span>same origin-domain</span></li>
+
+    <li>A <code>Window</code> and the <code>Window</code> that opened it</li>
+   </ul>
+
+   <p>The following pairs of global objects are <em>not</em> within the same <span>shared
+   environment settings objects</span>, and thus cannot share memory:</p>
+
+   <ul class="brief">
+    <li>A <code>Window</code> and a shared worker it creates</li>
+
+    <li>A worker (of any type) and a shared worker it creates</li>
+
+    <li>A <code>Window</code> and a service worker it creates</li>
+
+    <li>A <code>Window</code> and the <code>Window</code> of an <code>iframe</code> element that
+    cannot be <span>same origin-domain</span></li>
+   </ul>
+
+  </div>
+
   </div>