<?xml version="1.0" encoding="ISO-8859-1"?>

<!DOCTYPE ä [

<!ELEMENT ä ANY>
<!ATTLIST ä ö CDATA #IMPLIED>

<?ü aöü?>

<!NOTATION ß SYSTEM "xxx">
<!ENTITY Mß "mü">
]>

<!-- ÄÖÜ -->
<?ü äöü?>

<ä ö="éáí">
  <?ü µ?>
  &Mß;
  <ä ö="&Mß;"/>
  <!-- äöü -->
</ä>
<!-- ÄÖÜ -->
<?ü ß?>