function check_input (type,required,field) {
    if (required && field.value.length == 0) {
       field.className = 'required';
    } else if (!required && field.value.length == 0) {
       field.className = '';
    } else if (!validate_input(type,field.value)) {
       field.className = 'error';
    } else {
       field.className = 'ok';
    }
}

function validate_input(type, value) {
  switch (type) {
    case 'email':
      if (!value.match(/^[\w\.\-]+@([\w\-]+\.)+[a-zA-Z]+$/))
        return false;
      break;
    case 'ipv4':
      var ipPattern = /^(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})$/;
      if (!value.match(ipPattern))
        return false;
      for (i = 0; i < 4; i++) {
        thisSegment = ipArray[i];
        if (thisSegment > 255)
          return false;
      }
      break;
    case 'subdomain':
      if (!value.match(/^[\w\-\.]+$/))
         return false;
      break;
  }
  return true;
}