function postit(test){ //check postcode format is valid
 size = test.length;
 test = test.toUpperCase(); //Change to uppercase
 while (test.slice(0,1) == " ") //Strip leading spaces
  {test = test.substr(1,size-1);size = test.length
  }
 while(test.slice(size-1,size)== " ") //Strip trailing spaces
  {test = test.substr(0,size-1);size = test.length
  }
 test = test; //write back to form field
 if (size < 6 || size > 8){ //Code length rule
  alert(test + " is not a valid postcode - wrong length. Please check and try again.");
  return false;
  }
 if (!(isNaN(test.charAt(0)))){ //leftmost character must be alpha character rule
   alert(test + " is not a valid postcode - cannot start with a number. Please check and try again.");
   return false;
  }
 if (isNaN(test.charAt(size-3))){ //first character of inward code must be numeric rule
   alert(test + " is not a valid postcode. Please check and try again.");
   return false;
  }
 if (!(isNaN(test.charAt(size-2)))){ //second character of inward code must be alpha rule
   alert(test + " is not a valid postcode. Please check and try again.");
   return false;
  }
 if (!(isNaN(test.charAt(size-1)))){ //third character of inward code must be alpha rule
   alert(test + " is not a valid postcode. Please check and try again.");
   return false;
  }
 if (!(test.charAt(size-4) == " ")){//space in position length-3 rule
   alert(test + " is not a valid postcode - no space or space in wrong position.");
   return false;
   }
 count1 = test.indexOf(" ");count2 = test.lastIndexOf(" ");
 if (count1 != count2){//only one space rule
   alert(test + " is not a valid postcode - only one space allowed.");
   return false;
  }
return true;
}

function trim(s) {
  while (s.substring(0,1) == ' ') {
    s = s.substring(1,s.length);
  }
  while (s.substring(s.length-1,s.length) == ' ') {
    s = s.substring(0,s.length-1);
  }
  return s;
}

function checkForm(theForm){
	if (theForm.customertype.value==""){
		alert("Please select your customer type to continue.");
		return false;
	}
	else if (trim(theForm.productrange.value) == ""){
		alert("Please select your product range to continue.");
		theForm.productrange.focus();
		return false;
	}
	else if (postit(theForm.postcode.value)==false){
		//alert("Please enter your postcode.");
		theForm.postcode.focus();
		return false;
	}
	return true;
}