Clarify what happens with a failed pointer capture set/release. (#537)

Fixes #534. Implicit pointer capture state after a failed explicit capture call at pointerdown

index.html

@@ -1166,6 +1166,7 @@ <h2><dfn data-lt="set pointer capture">Setting pointer capture</dfn></h2>
                     the |element|'s [=Node/node document=] is not the <a>active document</a> of the |pointer|, then terminate these steps.</li>
                 <li>For the specified <code>pointerId</code>, set the <dfn>pending pointer capture target override</dfn> to the {{Element}} on which this method was invoked.</li>
             </ol>
+            <div class="note">If a call to set or release a pointer capture is made while a previous set or release call is in a pending state (see <a>process pending pointer capture</a>), the second call overrides the first call if the second call is successful, otherwise the first call remains effective.  This is true for a failed attempt to release an <a>implicit pointer capture</a> at a {{GlobalEventHandlers/pointerdown}} listener.</div>
         </section>
 
         <section>
@@ -1176,6 +1177,7 @@ <h2><dfn data-lt="release pointer capture">Releasing pointer capture</dfn></h2>
                 <li>If <a data-lt="Element.hasPointerCapture">hasPointerCapture</a> is false for the {{Element}} with the specified <code>pointerId</code>, then terminate these steps.</li>
                 <li>For the specified <code>pointerId</code>, clear the <a>pending pointer capture target override</a>, if set.</li>
             </ol>
+            <div class="note">See the note in the section <a>Setting pointer capture</a>.</div>
         </section>
 
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