Add two notes/clarifications to 2.1.1/2.1.3 understanding

understanding/20/keyboard-no-exception.html

@@ -29,6 +29,28 @@ <h2>Intent of Keyboard (No Exception)</h2>
          Rather, it means that content that uses path-dependent input cannot conform to this
          Success Criterion and therefore cannot meet Guideline 2.1 at Level AAA. 
       </p>
+
+      <div class="note">
+         <p>Platforms and user agents usually have conventions for how web content or applications
+            are controlled with a keyboard interface. As a best practice, content should follow
+            the platform/user agent conventions. However, deviating from these conventions does
+            not fail the normative requirement of this success criterion. For instance, buttons
+            that have focus can generally be activated using both the <kbd>Enter</kbd> key and
+            the <kbd>Space</kbd> bar. If a custom button control in a web application instead only
+            reacts to <kbd>Enter</kbd> (or even a completely custom key or key combination), this does <strong>not</strong> fail the Success Criterion.
+         </p>
+      </div>
+
+      <div class="note">
+         <p>This Success Criterion does not require that every visible control that can be activated
+            using a mouse or touch screen must also be focusable and actionable using the keyboard.
+            The normative requirement is only that there must be a way for keyboard users to perform
+            the same, or comparable, actions and to operate the content. Generally, the easiest way
+            to achieve this is to provide controls that can be operated with all possible input devices;
+            however, if a web application implements a completely separate mode of operation for keyboard
+            users, it will <strong>not</strong> fail the success criterion.
+         </p>
+      </div>
 
    </section>
 

understanding/20/keyboard.html

@@ -69,6 +69,27 @@ <h2>Intent of Keyboard</h2>
 
       </p>
 
+      <div class="note">
+         <p>Platforms and user agents usually have conventions for how web content or applications
+            are controlled with a keyboard interface. As a best practice, content should follow
+            the platform/user agent conventions. However, deviating from these conventions does
+            not fail the normative requirement of this success criterion. For instance, buttons
+            that have focus can generally be activated using both the <kbd>Enter</kbd> key and
+            the <kbd>Space</kbd> bar. If a custom button control in a web application instead only
+            reacts to <kbd>Enter</kbd> (or even a completely custom key or key combination), this does <strong>not</strong> fail the success criterion.
+         </p>
+      </div>
+
+      <div class="note">
+         <p>This success criterion does not require that every visible control that can be activated
+            using a mouse or touch screen must also be focusable and actionable using the keyboard.
+            The normative requirement is only that there must be a way for keyboard users to perform
+            the same, or comparable, actions and to operate the content. Generally, the easiest way
+            to achieve this is to provide controls that can be operated with all possible input devices;
+            however, if a web application implements a completely separate mode of operation for keyboard
+            users, it will <strong>not</strong> fail the success criterion.
+         </p>
+      </div>
 
    </section>
    <section id="benefits">
@@ -115,8 +136,12 @@ <h2>Examples of Keyboard</h2>
          <dd>A PDA device that is usually operated via a stylus has an optional keyboard that can
                be attached.  The keyboard allows full Web browsing in standard fashion.  The Web
                content is operable because it was designed to work with keyboard-only access.</dd>
+        <dt>Example 7: Simple search form with mouse-operable submit button</dt>
+        <dd>A search form includes a text input field followed by a submit button. The submit button itself
+               has been coded so that it does <em>not</em> receive focus, and can only be activated using the mouse.
+               However, since keyboard users can submit the search by pressing <kbd>Enter</kbd> in the text input
+               after typing their search terms, the form passes this Success Criterion.</dd>
       </dl>
-
    </section>
 
    <section id="resources">