Hi,

I have modified the script of willem slightly to exclude www. Check this.

var url=newValue;
var re = /^(http[s]?:\/\/){0,1}(www\.){0,1}[a-zA-Z0-9\.\-]+\.[a-zA-Z]{2,5}[\.]{0,1}/;
if(url.indexOf("www.") > -1 || !re.test(url)) {
    g_form.showFieldMsg('your field', 'invalid url');
    return false;
}