Update accompanying-document.xml

1.1/accompanying-texts/accompanying-document.xml

@@ -33,7 +33,7 @@
             <p>Here goes the text.</p>
          </div>
          
-         <!-- this is a marker for the serialization and mustn't be filled with content.
+         <!-- this is a marker for the serialization and must not be filled with content.
          it triggers the element specific listings of
             * further information
             * data values