The tag is present in Lintian version 2.104.232. That is the most recent version we know about.
The Document field in doc-base control file must be located at first line of the file. While unregistering documents, doc-base 0.8 and later parses only the first line of the control file for performance reasons.
Refer to Debian doc-base Manual section 22.214.171.124 for details.