document caveat regarding fieldset legend and #6199

docs/css.html

@@ -1759,7 +1759,8 @@ For example, <code><section></code> should be wrapped as inlin
 </pre>
           <p>
             <span class="label label-info">Heads up!</span>
-            <code>&lt;a&gt;</code> buttons within a <code>fieldset[disabled]</code> will be styled like they each had the <code>.disabled</code> class, but this only affects aesthetics; you must use custom JavaScript to actually make such links non-functional.
+            Contrary to the HTML5 spec, form controls within a <code>fieldset</code>'s <code>legend</code> will also be disabled.<br>
+            Also, <code>&lt;a&gt;</code> buttons within a <code>fieldset[disabled]</code> will be styled like they each had the <code>.disabled</code> class, but this only affects aesthetics; you must use custom JavaScript to actually make such links non-functional.
           </p>
 
           <h3>Validation states</h3>

docs/templates/pages/css.mustache

@@ -1699,7 +1699,8 @@ For example, <code><section></code> should be wrapped as inlin
 </pre>
           <p>
             <span class="label label-info">Heads up!</span>
-            <code>&lt;a&gt;</code> buttons within a <code>fieldset[disabled]</code> will be styled like they each had the <code>.disabled</code> class, but this only affects aesthetics; you must use custom JavaScript to actually make such links non-functional.
+            Contrary to the HTML5 spec, form controls within a <code>fieldset</code>'s <code>legend</code> will also be disabled.<br>
+            Also, <code>&lt;a&gt;</code> buttons within a <code>fieldset[disabled]</code> will be styled like they each had the <code>.disabled</code> class, but this only affects aesthetics; you must use custom JavaScript to actually make such links non-functional.
           </p>
 
           <h3>Validation states</h3>