How to add tooltip text to element in XUL

Question

I have the following XBL document.

            <?xml version="1.0" encoding="UTF-8"?>
            <!DOCTYPE window [
              <!ENTITY % commonDTD SYSTEM "chrome://titlemanager/locale/default.dtd">
              %commonDTD;
              <!ENTITY % productwindowDTD SYSTEM "chrome://titlemanager/locale/product.dtd">
              %productwindowDTD;
            ]>
            <?xml-stylesheet href="chrome://titlemanager/skin/default.css" type="text/css"?>
            <bindings xmlns="http://www.mozilla.org/xbl"
                      xmlns:xbl="http://www.mozilla.org/xbl"
                     xmlns:xul="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
                     xmlns:html="http://www.w3.org/1999/xhtml">
                <binding id="productpage">
                    <content> 
                        <html:div class="maincontainerproduct" tooltiptext="testDiv">               
                        </html:div>
                    </content>
                </binding>
            </bindings>

But in the div, I am not able to apply the tooltiptext property in the element.