More substantial elaborations

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@@ -90366,10 +90366,11 @@ import "https://example.com/foo/../module2.mjs";</code></pre>
   <h5>Integration with the JavaScript agent cluster formalism</h5>
 
   <p>JavaScript also defines the concept of an <span>agent cluster</span>, which this standard maps
-  to the web platform using the <dfn>can share memory with</dfn> equivalence relation detailed
-  below. On the web platform, an <span>agent cluster</span> consists of all <span
-  data-x="agent">agents</span> in the same equivalence class with respect to the <span>can share
-  memory with</span> equivalence relation.</p>
+  to the web platform using the <span>can share memory with</span> equivalence relation detailed
+  below, as well as explicit allocation of <span data-x="similar-origin window agent">similar-origin
+  window agents</span> to agent clusters. On the web platform, an <span>agent cluster</span>
+  consists of all <span data-x="agent">agents</span> in the same equivalence class with respect to
+  the <span>can share memory with</span> equivalence relation.</p>
 
   <p>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
@@ -90382,6 +90383,13 @@ import "https://example.com/foo/../module2.mjs";</code></pre>
   implemented in user agents. By enforcing these idealized divisions at the specification level, we
   ensure that web developers see interoperable behavior with regard to shared memory, even in the
   face of varying and changing user agent process models.</p>
+
+  <hr>
+
+  <p>The following defines the allocation of the <span data-x="agent cluster">agent clusters</span>
+  of <span data-x="similar-origin window agent">similar-origin window agents</span>.</p>
+
+
   <p>A <dfn data-export="">scheme-and-site</dfn> is a <span>tuple</span> of a <span
   data-x="concept-url-scheme">scheme</span> and a <span data-x="concept-domain">domain</span>.</p>
 
@@ -90446,6 +90454,18 @@ import "https://example.com/foo/../module2.mjs";</code></pre>
    <li><p>Return <var>group</var>'s <span>agent cluster map</span>[<var>key</var>].</p></li>
   </ol>
 
+  <p class="note">This means that there is only one <span>similar-origin window agent</span> per
+  browsing context agent cluster. (However, other types of agents might be in the same cluster, if
+  they <span>can share memory with</span> the similar-origin window agent.)</p>
+
+  <hr>
+
+  <p>The allocation of other types of agents to agent clusters is done via the following <dfn>can
+  share memory with</dfn> equivalence relation. Until such a time that this standard has a better
+  handle on the lifetimes of those sorts of agents, user agents must allocate new agent clusters, or
+  reuse ones created via <span data-x="obtain-browsing-agent-cluster">obtain a browsing context
+  agent cluster</span>, in order to ensure that there is an agent cluster for each equivalence class
+  of <span>can share memory with</span>.</p>
 
   <p>A <span>similar-origin window agent</span>, <span>dedicated worker agent</span>, <span>shared
   worker agent</span>, or <span>service worker agent</span>, <var>agent</var>, <span>can share