Bison 2.2 exception to GPL 2.0 or later

As a special exception, you may create a larger work that contains part or all
of the Bison parser skeleton and distribute that work under terms of your
choice, so long as that work isn't itself a parser generator using the skeleton
or a modified version thereof as a parser skeleton.  Alternatively, if you
modify or redistribute the parser skeleton itself, you may (at your option)
remove this special exception, which will cause the skeleton and the resulting
Bison output files to be licensed under the GNU General Public License without
this special exception.

This special exception was added by the Free Software Foundation in version 2.2
of Bison.