Specify br and wbr rendering as magic

Closes #2291.

source

@@ -109512,9 +109512,8 @@ del, s, strike { text-decoration: line-through; }
 q::before { content: open-quote; }
 q::after { content: close-quote; }
 
-<span data-x="" id="br-wbr-content">br { display-outside: newline; } /* <a href="#bidi-rendering">this also has bidi implications</a> */
+<span data-x="" id="br-wbr-content">
 nobr { white-space: nowrap; }
-wbr { display-outside: break-opportunity; } /* <a href="#bidi-rendering">this also has bidi implications</a> */
 nobr wbr { white-space: normal; }</span></pre>
 
   <p>The following rules are also expected to apply, as
@@ -109677,6 +109676,11 @@ br[clear=all i], br[clear=both i] { clear: both; }</pre>
 
   </ol>
 
+  <hr>
+
+  <p>The rendering of the <code>br</code> and <code>wbr</code> elements is also described in the <a
+  href="#widgets">Widgets</a> section.</p>
+
 
   <h4 id="bidi-rendering">Bidirectional text</h4>
 
@@ -109699,9 +109703,7 @@ input[dir=auto i]:matches([type=search i], [type=tel i], [type=url i],
 [type=email i]), textarea[dir=auto i], pre[dir=auto i] {
   unicode-bidi: plaintext;
 }
-/* see prose for input elements whose type attribute is in the Text state */
-
-/* the <a href="#br-wbr-content">rules setting the 'content' property</a> on <code>br</code> and <code>wbr</code> elements also has bidi implications */</pre>
+/* see prose for input elements whose type attribute is in the Text state */</pre>
 
   <p>When an <code>input</code> element's <code data-x="attr-dir">dir</code> attribute is in the
   <span data-x="attr-dir-auto">auto</span> state and its <code data-x="attr-input-type">type</code>
@@ -110714,9 +110716,43 @@ object[align=bottom i] {
 
   <div w-nodev>
 
+  <h4>The <code>br</code> and <code>wbr</code> elements</h4>
+
+  <p>The <code>br</code> element is expected to render as a line break, ignoring the effect of the
+  <span>'white-space'</span> property.</p>
+
+  <p>The <code>wbr</code> element is expected to render as a line break opportunity.</p>
+
+  <p>No CSS properties are expected to affect the rendering of these elements.</p>
+
+  <div class="note">
+   <p>The following CSS snippet reproduces the above expectations:</p>
+
+   <pre class="css">@namespace url(http://www.w3.org/1999/xhtml);
+
+br {
+  all: unset !important;
+  display: contents !important;
+  content: "\A" !important;
+  white-space: pre !important;
+}
+wbr {
+  all: unset !important;
+  display: contents !important;
+  content: "\200B" !important;
+}</pre>
+
+   <p>However, this is not part of the user agent stylesheet rules, as inspecting the used style
+   of <code>br</code> and <code>wbr</code> elements does not give any of the above values.</p>
+
+   <p>(Note also that this depends on the as-of-yet unimplemented ability to specify the
+   <span>'content'</span> property on elements, instead of just on the <code
+   data-x="">::before</code> and <code data-x="">::after</code> pseudo-elements.)</p>
+  </div>
+
   <h4>The <code>button</code> element</h4>
 
-  <p>The <code>button</code> element expected to render as an <span>'inline-block'</span> box
+  <p>The <code>button</code> element is expected to render as an <span>'inline-block'</span> box
   depicting a button whose contents are the contents of the element.</p>
 
   <p>When the <code>button</code> element's <code data-x="attr-button-type">type</code> attribute is