function vldFrm_Guestbook()
{
   var vname, vemail, vurl, vmessage;
   var result = true;
   var msg="";

   with(window.document.frmGuestbook)
   {
      vname    = name.value;
      vemail   = email.value;
      vurl     = url.value;
      vmessage = message.value;
   }

   // if name is empty alert the visitor
   if(trim(vname) == "")
   {
      msg+="Please include your name!\n";
	  result = false;
   }
   if( (trim(vemail) == "") || !isEmail(trim(vemail)) )
   {
     msg+="Please enter a valid email address!\n";
     result = false;
   }
   if( (trim(vurl) != "") && !isURL(trim(vurl)) )
   {
     msg+="Please enter a valid URL or leave the field empty!\n";
     result = false;
   }
   if( trim(vmessage) == '' )
   {
     msg+="Please enter your story or comment!\n";
     result = false;
   }
   if(msg==""){
	  return result;
   }{
	 alert(msg)
	 return result;
   }
}
/*
   Strip whitespace from the beginning and end of a string
*/
function trim(str)
{
   return str.replace(/^\s+|\s+$/g,'');
}
/*
   Check if a string is in valid email format. 
*/
function isEmail(str)
{
var regex = /^[-_.a-z0-9]+@(([-a-z0-9]+\.)+(ad|ae|aero|af|ag|ai|al|am|an|ao|aq|ar|arpa|as|at|au|aw|az|ba|bb|bd|be|bf|bg|bh|bi|biz|bj|bm|bn|bo|br|bs|bt|bv|bw|by|bz|ca|cc|cd|cf|cg|ch|ci|ck|cl|cm|cn|co|com|coop|cr|cs|cu|cv|cx|cy|cz|de|dj|dk|dm|do|dz|ec|edu|ee|eg|eh|er|es|et|eu|fi|fj|fk|fm|fo|fr|ga|gb|gd|ge|gf|gh|gi|gl|gm|gn|gov|gp|gq|gr|gs|gt|gu|gw|gy|hk|hm|hn|hr|ht|hu|id|ie|il|in|info|int|io|iq|ir|is|it|jm|jo|jp|ke|kg|kh|ki|km|kn|kp|kr|kw|ky|kz|la|lb|lc|li|lk|lr|ls|lt|lu|lv|ly|ma|mc|md|mg|mh|mil|mk|ml|mm|mn|mo|mp|mq|mr|ms|mt|mu|museum|mv|mw|mx|my|mz|na|name|nc|ne|net|nf|ng|ni|nl|no|np|nr|nt|nu|nz|om|org|pa|pe|pf|pg|ph|pk|pl|pm|pn|pr|pro|ps|pt|pw|py|qa|re|ro|ru|rw|sa|sb|sc|sd|se|sg|sh|si|sj|sk|sl|sm|sn|so|sr|st|su|sv|sy|sz|tc|td|tf|tg|th|tj|tk|tm|tn|to|tp|tr|tt|tv|tw|tz|ua|ug|uk|um|us|uy|uz|va|vc|ve|vg|vi|vn|vu|wf|ws|ye|yt|yu|za|zm|zw)|(([0-9][0-9]?|[0-1][0-9][0-9]|[2][0-4][0-9]|[2][5][0-5])\.){3}([0-9][0-9]?|[0-1][0-9][0-9]|[2][0-4][0-9]|[2][5][0-5]))$/i;
return regex.test(str);
}

/*
   Check if a string is a valid http URL
*/
function isURL(str){ 
    var RegExp = /^(([\w]+:)?\/\/)?(([\d\w]|%[a-fA-f\d]{2,2})+(:([\d\w]|%[a-fA-f\d]{2,2})+)?@)?([\d\w][-\d\w]{0,253}[\d\w]\.)+[\w]{2,4}(:[\d]+)?(\/([-+_~.\d\w]|%[a-fA-f\d]{2,2})*)*(\?(&?([-+_~.\d\w]|%[a-fA-f\d]{2,2})=?)*)?(#([-+_~.\d\w]|%[a-fA-f\d]{2,2})*)?$/; 
    if(RegExp.test(str)){ 
        return true; 
    }
	else{ 
        return false; 
    } 
}