Trying to get an overview of the LaTeX source code base

[Karl Berry]

     KerTeX (restricted to a BSD license and 
    therefore suitable in places that GPL code is not acceptable).

KerTeX's license has an advertising clause (like original BSD) that
makes it incompatible with all copyleft licenses, and probably
unacceptable in practice for the big app stores or anywhere else
"commercial". https://kertex.kergis.com/en/license.html

That is not what most people think of as the "BSD license" (for several
decades now), which is modified BSD, that is, modified specifically to
remove the advertising clause.

Happily, Thierry agreed to release the Prote extensions under the
standard MIT/X11 license (like XeTeX), so Martin could use them in HiTeX. -k