Add an example of a non-HTML/SVG element

Closes #4232.

This also excludes the sentence "Features shared between HTML and SVG
elements use the HTMLOrSVGElement interface mixin: [SVG]" from the
developer's edition, since the IDL for HTMLOrSVGElement is not shown
anyway.

Author: domenic

source

@@ -10324,8 +10324,6 @@ interface <dfn>HTMLUnknownElement</dfn> : <span>HTMLElement</span> {
   a linear transition of the element's prototype chain, from <code>HTMLElement</code> to a subclass,
   instead of a lateral one, from <code>HTMLUnknownElement</code> to an unrelated subclass.</p>
 
-  </div>
-
   <p>Features shared between HTML and SVG elements use the <code>HTMLOrSVGElement</code> interface
   mixin: <ref spec=SVG></p>
 
@@ -10339,6 +10337,16 @@ interface <dfn>HTMLUnknownElement</dfn> : <span>HTMLElement</span> {
   void <span data-x="dom-blur">blur</span>();
 };</code></pre>
 
+  </div>
+
+  <div class="example">
+   <p>An example of an element that is neither an HTML nor SVG element is one created as
+   follows:</p>
+
+   <pre><code class="html" data-x="">const el = document.createElementNS("some namespace", "example");
+console.assert(el.constructor === Element);</code></pre>
+  </div>
+
   <div w-nodev>
 
   <h4 id="html-element-constructors">HTML element constructors</h4>