I love this

   function returnFalse ()       {return false}

and the fact that their home cooked date_val() function does not use their home cooked isLeapYear() and daysInMonth() functions, but uses its own, pretty much unreadable, leap year determination algorithm.

   var l_k=parseInt(l_y%100)
   var l_m=parseInt(l_y/100)
   if (l_d == 29 && ((l_y/4)!=parseInt(l_y/4)))
   {
    l_err=1 ;
    l_errstring = "Date is invalid.";
   }

   if(l_k ==0){
    if (l_d == 29 && ((l_m/4)!=parseInt(l_m/4)))
    {
     l_err=1 ;
     l_errstring = "Date is invalid.";
    }
   }