add pageup/pagedown

source

@@ -53871,8 +53871,9 @@ interface <dfn interface>HTMLSelectElement</dfn> : <span>HTMLElement</span> {
   data-x="event-keydown">keydown</code> event will prevent the new <code>option</code> from being
   focused.</p>
 
-  <p class="note">Implementations commonly allow the user to choose the next or previous option via
-  the arrow-up and arrow-down keys, or pick the first or last option via the Home or End keys.</p>
+  <p class="note">Implementations commonly allow the user to focus the next or previous option via
+  the arrow-up and arrow-down keys, focus the first or last option via the Home or End keys, or
+  focus the first or last option in the viewport of the picker via the PageUp or PageDown keys.</p>
 
   <p>If the <code data-x="attr-select-multiple">multiple</code> attribute is present, and the
   element is not <span data-x="concept-fe-disabled">disabled</span>, then the user agent should