add asserts/issue

source

@@ -77158,6 +77158,10 @@ dictionary <dfn>DragEventInit</dfn> : <span>MouseEventInit</span> {
    <li><p>Let <var>browsingContext</var> be the result of <span>creating a new browsing
    context</span> with <var>opener</var>'s <span>active document</span>.</p></li>
 
+   <li><p>Assert: <var>opener</var>'s <span>top-level browsing context</span>'s <span data-x="tlbc
+   group">group</span> is non-null, as <span data-x="navigate">navigating</span> invokes this
+   directly.</p></li>
+
    <li><p><span data-x="bcg append">Append</span> <var>browsingContext</var> to <var>opener</var>'s
    <span>top-level browsing context</span>'s <span data-x="tlbc group">group</span>.</p></li>
 
@@ -77695,6 +77699,10 @@ console.assert(iframeWindow.frameElement === null);
   <var>browsingContext</var>, run these steps:</p>
 
   <ol>
+   <li><p>Assert: <var>browsingContext</var>'s <span data-x="tlbc group">group</span> is non-null,
+   because a <span>browsing context</span> only gets <span data-x="a browsing context is
+   discarded">discarded</span> once.</p></li>
+
    <li><p>Let <var>group</var> be <var>browsingContext</var>'s <span data-x="tlbc
    group">group</span>.</p></li>
 
@@ -89005,11 +89013,18 @@ import "https://example.com/foo/../module2.mjs";</code></pre>
   these steps:</p>
 
   <ol>
-   <li><p>If <var>A</var>'s <span>relevant settings object</span>'s <span>responsible browsing
-   context</span>'s <span>top-level browsing context</span>'s <span data-x="tlbc group">group</span>
-   is not <var>B</var>'s <span>relevant settings object</span>'s <span>responsible browsing
-   context</span>'s <span>top-level browsing context</span>'s <span data-x="tlbc
-   group">group</span>, then return false.</p></li>
+   <li>
+    <p>If <var>A</var>'s <span>relevant settings object</span>'s <span>responsible browsing
+    context</span>'s <span>top-level browsing context</span>'s <span data-x="tlbc
+    group">group</span> is not <var>B</var>'s <span>relevant settings object</span>'s
+    <span>responsible browsing context</span>'s <span>top-level browsing context</span>'s <span
+    data-x="tlbc group">group</span>, then return false.</p>
+
+    <p class="&#x0058;&#x0058;&#x0058;">Unfortunately this model falls apart the moment a
+    <span>browsing context</span> is <span data-x="a browsing context is
+    discarded">discarded</span>. <a href="https://github.com/whatwg/html/issues/4361">Issue
+    #4361</a> sketches a setup that could improve this situation.</p>
+   </li>
 
    <li><p>Let <var>originA</var> be <var>A</var>'s <span>relevant settings object</span>'s <span
    data-x="concept-settings-object-origin">origin</span> and <var>originB</var> be <var>B</var>'s