/usr/share/doc/libnanoxml2-java/examples/Java/Chapter04-04/document.dtd is in libnanoxml2-java-doc 2.2.3.dfsg-5.
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The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 | <!ELEMENT Chapter (Paragraph*)>
<!ATTLIST Chapter
title CDATA #REQUIRED
id CDATA #REQUIRED>
<!ELEMENT Paragraph (#PCDATA)>
<!ATTLIST Paragraph
align (left|center|right) 'left'>
|