function checkPostCode(fieldno, event, postcode1, postcode2) 
{
	var charKey;
	var specKey;
	var exp;

	if (event.type == 'paste') 
	{
		charKey = clipboardData.getData("Text");
	} 
	else if (event.type == 'keydown') 
	{
		charKey = getAlfaNumPressed(event);
		specKey = getSpecialKeyPressed(event);
		if (charKey == null && specKey == null) 
		{
			return false;
		} 
	}

	if (charKey != null) 
	{
		switch (fieldno) 
		{
			case 1:
				exp = /[^0-9]/;    //numeric part: accept digits only
				break; 
			case 2:
				exp = /[^a-zA-Z]/; //alfabetic part: accept letters a-z and A-Z only
				break;
		} 
		if (exp.test(charKey)) 
		{
			return false;
		}
	}

	// Clear postcode fields if they were already completed		
	if (fieldno == 1) 
	{
		if (charKey != null || specKey == "Delete" || specKey == "Backspace") 
		{
			if ((postcode1 != null && postcode2 != null) && (!postcode1.readOnly && !postcode2.readOnly) && (postcode1.value.length == postcode1.maxLength && postcode2.value.length == postcode2.maxLength)) 
			{ 
				postcode1.value = "";
				postcode2.value = "";
			}
		}
	}
	return true;
}

//function that shifts focus when needed
function nextField(obj, event, nextFld) 
{
	if (getSpecialKeyPressed(event) != null) 
	{
		return;
	}
	if(obj.value.length == obj.maxLength) 
	{
		document.getElementById(nextFld).focus();
	}
}