function validateDigits(strCont) {
      if (strCont.length !=  11) {
         return false;
      }
      else {
         var test = strCont.search(/[A-Za-z]{4}[0-9]+/g);
         if (test != -1) {
            return true;
         }
         else {
            return false;
         }
      }
   }

   function checkForm() {

      var search_type = document.ctform.search_type.options[document.ctform.search_type.selectedIndex].value;
      var regExp = /^[A-Z]{2,}[A-Z0-9]{3,}$/;

      if (document.ctform.search_for.value == '') {
         alert('Please enter a container number OR a Bill of Lading.');
         return false;
      }

      if (search_type == 'cn') {
         if (!validateDigits(document.ctform.search_for.value)) {
            alert('Please enter a valid container number.');
            document.ctform.search_for.focus();
            return false;
         }
      }


      if (search_type == 'bl') {
         if (document.ctform.search_for.value.length < 9 || document.ctform.search_for.value.length > 12) {
            alert('Please enter a valid BL number.');
            document.ctform.search_for.focus();
            return false;
         }
         else if (!(regExp.test(document.ctform.search_for.value))){
            alert('Please enter a valid BL number.');
            return false;
         }
      }

      return true;
   }