Why is quran package installed by default on Texlive2020

[Karl Berry]

Hi Zdenek,

    IMHO collection-xetex should contain files for the formats (plain
    XeTeX, XeLaTeX), polyglossia, fontspec and possibly a few more
    packages needed generally for use with the XeTeX engine.

Sorry, that doesn't work, because collections partition all the
packages, as has been said a couple times already. fontspec does not
work *only* with xetex, as you know.

So the general purpose of c-xetex (and c-luatex) is not to provide the
engine and "core packages", natural as that sounds. Rather, it is to
provide packages that work with only the given engine. So that if
someone does not have or want XeTeX, they don't have to end up with
XeTeX-only packages either. c-xetex includes both the engine and such
packages.

To add more complication, XeTeX and LuaTeX aren't parallel any more
(though they were for some years). LuaTeX, or rather TeXLua, has since
become an integral part of the system, so it has to be (and is) in
c-basic. On the other hand, people might not ever want to typeset with
luatex ("[pdf]tex is good enough for me"), so again, c-luatex is
intended to be packages that only work with luatex.

The {Xe,Lua}LaTeX formats add yet another layer of complication. I'm not
going to try to describe what I've done there. It's the best I can come
up with.

As has happened with quran, I'm sure some packages have gained support
for the other engine since they were first releases and thus are
misclassified now. I don't try to track that specifically (sometimes I
happen to notice), since it makes little difference in practice, but
just wait for user reports ... as you did here. --best, karl.