// Assign the event handlers
if (typeof window.event != 'undefined') {
    document.onkeydown = cancelBack;
} else {
    document.onkeypress = cancelBack;
}

function cancelBack(evt) {
 var keynum;
 var retValue = true;
 var evt = (evt) ? evt : ((window.event) ? window.event : "");
 if (evt) {
  var elem;
  if (evt.target) {
	elem = evt.target;
    keynum = evt.which;
  } else {
	elem = evt.srcElement;
    keynum = evt.keyCode;
  }
  if (elem) {
   if ((keynum == 8 || (keynum == 37 && evt.altKey) || (keynum == 39 && evt.altKey)) && (!(elem.type == 'textarea' || elem.type == 'text' || elem.type == 'password')) ) {
    evt.cancelBubble = true;
    evt.returnValue = false;
    evt.stopPropagation();
    evt.preventDefault();
    retValue = false;
   }
  }
 }
 return retValue;
}