PAC File - Bypass proxy server for local addresses

Hi,
Ive got a pac file done which looked like this (example a) what Im trying to get is a pac file that bypasses local addresses.  Any ideas on how this can be done. Ive tried (example b) but does anyone know if this is the right way?

Thanks

example a)
function
	FindProxyForURL(URL,host)
	{
	return "PROXY 10.4.2.28:80;PROXY 10.4.2.29:80";
	}
 
example b)
function FindProxyForURL(url, host)
{
if (shExpMatch(url, "*.internaldomainname.co.uk")) 
return DIRECT;
else
return "PROXY 10.4.2.29:80;PROXY 10.4.2.28:80";
}

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