The tag is present in Lintian version 2.104.232. That is the most recent version we know about.
The short description of a boolean debconf template should be phrased in the form of a question which should be kept short and should generally end with a question mark. Terse writing style is permitted and even encouraged if the question is rather long.
If this template is only used internally by the package and not displayed to the user, put "for internal use" in the short description.
Refer to Debian Developer's Reference section 18.104.22.168.2 for details.