Tabs Pattern: Revise guidance on focusing tabpanel for issue 1164 (pull

#1274)

Resolves #1164 by Changing the Tab key description in the keyboard subsection of the tabs pattern.
Guidance now suggests that the tabpanel should be focused unless the first element containing meaningful content in the tabpanel is focusable.

Co-authored-by: Matt King <a11yThinker@Gmail.com>

aria-practices.html

@@ -1024,7 +1024,7 @@ <h4>WAI-ARIA Roles, States, and Properties</h4>
           <li>The element that serves as an input and displays the combobox value has role <a href="#combobox" class="role-reference">combobox</a>.</li>
           <li>
             The combobox element has <a href="#aria-controls" class="property-reference">aria-controls</a> set to a value that refers to the element that serves as the popup.
-            Note that <code>aria-controls</code> only needs to be set when the popup is visible. However, it is valid to reference an element that is not visible. 
+            Note that <code>aria-controls</code> only needs to be set when the popup is visible. However, it is valid to reference an element that is not visible.
           </li>
           <li>The popup is an element that has role <a href="#listbox" class="role-reference">listbox</a>, <a href="#tree" class="role-reference">tree</a>, <a href="#grid" class="role-reference">grid</a>, or <a href="#dialog" class="role-reference">dialog</a>.</li>
           <li>
@@ -2632,8 +2632,11 @@ <h4>Keyboard Interaction</h4>
         <p>For the tab list:</p>
         <ul>
           <li>
-            <kbd>Tab</kbd>: When focus moves into the tab list, places focus on the active <code>tab</code> element.
-            When the tab list contains the focus, moves focus to the next element in the page tab sequence outside the tablist, which is typically either the first focusable element inside the tab panel or the tab panel itself.
+            <kbd>Tab</kbd>:
+            <ul>
+              <li>When focus moves into the tab list, places focus on the active <code>tab</code> element.</li>
+              <li>When the tab list contains the focus, moves focus to the next element in the page tab sequence outside the tablist, which is the tabpanel unless the first element containing meaningful content inside the tabpanel is focusable.</li>
+            </ul>
           </li>
           <li>When focus is on a tab element in a horizontal tab list:
             <ul>