If you want to track clicks on your main html banner
add this code to onclick event to your a href tag.
onclick="javascript:parent.ExpandableBanners.calcClicks(parent.enter_banner_name);"
where 'enter_banner_name' is the name of your expandable banner.Make sure that you replace the spaces in name with '_'.
If you want to add the close button inside the banner use this.
<a href="javascript:ExpandableBanners.closeAd('enter_your_banner');">Click here to close</a>
