As per https://metacpan.org/release/RAAB/SGMLSpm-1.1/source/lib/SGMLS.pm (and the missing or-later-statement) LICENSE is GPL-2 Reproducible: Always
At first glance, I agreed with you, but... DOC/sgmlspl.sgml has: ``` [...] <para>Welcome to &sgmlspl;, a simple sample &perl5; application which uses the &sgmls.pm; class library.</para> <important id=terms> <title>Terms</title> <para>This program, along with its documentation, is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.</para> [...] ``` See also elisp/sgmls.el, script/sgmlspl.pl, lib/sgmlspl-specs/skel.pl.
(which would make it GPL-2 GPL-2+ for now, in lieu of clarification from upstream)
I agree.