The tag is present in Lintian version 2.104.244. That is the most recent version we know about.
The Debian portion of the package version contains a reference to a particular Debian release or distribution. This should only be done for uploads targeted at a particular release, not at unstable or experimental, and should refer to the release by version number or code name.
Using "testing" or "stable" in a package version targeted at the current testing or stable release is less informative than using the code name or version number and may cause annoying version sequencing issues if the package doesn't change before the next release cycle starts.
Refer to Debian Developer's Reference section 5.14.3 for details.