/usr/share/avahi/avahi-service.dtd is in avahi-daemon 0.7-3.1ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 | <!ELEMENT service-group (name,service+)>
<!ATTLIST service-group>
<!ELEMENT name (#PCDATA)>
<!ATTLIST name replace-wildcards (yes|no) "no">
<!ELEMENT service (type,subtype*,domain-name?,host-name?,port,txt-record*)>
<!ATTLIST service protocol (ipv4|ipv6|any) "any">
<!ELEMENT type (#PCDATA)>
<!ATTLIST type>
<!ELEMENT subtype (#PCDATA)>
<!ATTLIST subtype>
<!ELEMENT domain-name (#PCDATA)>
<!ATTLIST domain-name>
<!ELEMENT host-name (#PCDATA)>
<!ATTLIST host-name>
<!ELEMENT port (#PCDATA)>
<!ATTLIST port>
<!ELEMENT txt-record (#PCDATA)>
<!ATTLIST txt-record value-format (text|binary-hex|binary-base64) "text">
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