function check_street(field) {
   var f = field.value;f = f.toLowerCase();f = f.replace('.','');f = f.replace(' ','');
   if (f.match('box') || f.match('apo') || f.match('po')) {
     alert('Warning: We are unable to ship to PO Boxes or APO addresses. We apologize for any inconvenience. ' + "\n\n" + 'If the address entered is not a PO Box or APO address you can ignore this warning.');
   }
 }