Editorial: clarify focusability wording and table styles

* Add a solid line to the top of the focusability examples table, to
  match the one at the end, and make it clearer to see that the example
  panels are part of the table.
* Add "and be sequentially focusable" before the list of elements that
  it is suggested browsers include in the "tab" order by default (when
  their tabindex value is null).

Closes #5087.

source

@@ -81,6 +81,13 @@
    #table-example-1 tbody td:first-child + td ~ td { width: 2.5em; }
    #table-example-1 tbody td:first-child + td + td + td ~ td { width: 1.25em; }
 
+   #table-fa { border-top: solid; }
+   #table-fa .example {
+     margin: 2em 0 1.5em 0;
+     padding: 1em 1em;
+   }
+   #table-fa .example::before { display: block; }
+
    .apple-table-examples { border: none; border-collapse: separate; border-spacing: 1.5em 0em; width: 40em; margin-left: 3em; }
    .apple-table-examples * { font-family: "Times", serif; }
    .apple-table-examples td, .apple-table-examples th { border: none; white-space: nowrap; padding-top: 0; padding-bottom: 0; }
@@ -72149,7 +72156,8 @@ END:VCARD</pre>
     <span>shadow-including tree order</span>.</p>
 
     <p>Modulo platform conventions, it is suggested that the following elements should be considered
-    as <span data-x="focusable area">focusable areas</span>:</p>
+    as <span data-x="focusable area">focusable areas</span> and be <span>sequentially
+    focusable</span>:</p>
 
     <ul>
      <li><code>a</code> elements that have an <code data-x="attr-hyperlink-href">href</code>
@@ -121421,6 +121429,7 @@ INSERT INTERFACES HERE
   Matthew Noorenberghe,
   Matthew Raymond,
   Matthew Thomas,
+  Matthew Tylee Atkinson, <!-- matatk on GitHub -->
   Mattias Waldau,
   Max Romantschuk,
   Menachem Salomon,