This is a cross-tool approach to identifying generated code. Some tools, notably phabricator, handle this marker specially. See https://reviews.freebsd.org/differential/diff/42870/ for such an example.
$FreeBSD$ This directory tree contains tools used for the maintenance and testing of FreeBSD. There is no toplevel Makefile structure since these tools are not meant to be built as part of the standard system, though there may be individual Makefiles in some of the subdirs. Please read the README files in the subdirs for further information.