The ace:autoCompleteEntry component uses the following markup structure, which nests a DIV inside of a SPAN, which is technically invalid for xhtml:

<div id="frm:autoCompleteAccessKey">
           <span style="display:inline-block;">
                <input accesskey="c" aria-autocomplete="list" autocomplete="off" class="ui-inputfield ui-widget ui-state-default ui-corner-all ui-state-optional" name="frm:autoCompleteAccessKey_input" onblur="" onfocus="ice.setFocus(this.id);" onmousedown="this.focus();" role="textbox" style="width: 150px;null" type="text" />

 **** <span style="position:relative;display:block;">
 **** <div class="ui-widget ui-widget-content ui-corner-all" id="frm:autoCompleteAccessKey_div"
                 style="display:none;z-index:500;">
               </div>
             </span>
           </span>
           <script type="text/javascript">
           </script>
           <span id="frm:autoCompleteAccessKey_fieldupdate">
             <script type="text/javascript">
             </script>
           </span>
           <div id="frm:autoCompleteAccessKey_update">
             <span>
               <script type="text/javascript">
               </script>
             </span>
           </div>
         </div>


This JIRA is to modify the markup to not nest a DIV inside a SPAN so improve XHTML compliance.