function sentered(urel, sizex, sizey){
 var posx = (screen.width / 2) - (sizex / 2);
 var posy = (screen.height / 2) - (sizey / 2);
 window.open(urel, 'okno', 'toolbar=no,location=no,directories=no,status=no,menubar=no,scrollbars=yes,resizable=no,copyhistory=no,width=' + sizex + ',height=' + sizey + ',left=' + posx + ',top=' + posy);
 return true;
}

function sentered_named(urel, sizex, sizey, name){
 var posx = (screen.width / 2) - (sizex / 2);
 var posy = (screen.height / 2) - (sizey / 2);
 window.open(urel, name, 'toolbar=no,location=no,directories=no,status=no,menubar=no,scrollbars=yes,resizable=no,copyhistory=no,width=' + sizex + ',height=' + sizey + ',left=' + posx + ',top=' + posy);
 return false;
}

function sentered_noscroll(urel, sizex, sizey){
 var posx = (screen.width / 2) - (sizex / 2);
 var posy = (screen.height / 2) - (sizey / 2);
 window.open(urel, 'okno', 'toolbar=no,location=no,directories=no,status=no,menubar=no,scrollbars=no,resizable=no,copyhistory=no,width=' + sizex + ',height=' + sizey + ',left=' + posx + ',top=' + posy);
 return false;
}

function is_email(email) {
  var emailPattern = /^[a-z0-9]+([_|-|.][a-z0-9]+)*\@([a-z0-9]+((-*)(.*)[a-z0-9]+)*\.(com|edu|biz|org|gov|int|info|mil|net|arpa|name|museum|coop|aero|[a-z][a-z])|(\[\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\]))$/;                     
  return emailPattern.test(email.toLowerCase());
}

function sprawdz_email(pole) {
  if (!is_email(pole.value)) {
    alert('Podany e-mail jest niepoprawny.');
    pole.focus();
    pole.select();
	return false;
  }
  return true;
}