[Fontinst] naming font definition files

[Dr. Clea F. Rees]

This is not strictly a fontinst issue but this list seemed more
appropriate than the others I'm aware of. But please let me know if I
should redirect the question.

Could somebody either tell me or point me to documentation which
explains the requirements for naming font definition files?

For example, suppose I have a font and font family called ArrowsADF and
the family has encoding U. Then in effect, I tell LaTeX to load
U/ArrowsADF/m/n, say. What determines the name of the font definition
file searched for and/or how should that file be named?

Originally, I used uArrowsADF.fd. This works fine for me but it turns
out not to work everywhere. Experimentation suggests that uarrowadf.fd
works elsewhere but whether that works everywhere is a further question.

Because it seems that what works here doesn't work elsewhere (and also
because I'm curious :), I'd like to understand what's happening so that
I have at least a fighting chance of using names which work everywhere.

Looking at the log file sent from elsewhere (Debian, I think), LaTeX
seemed to search for UArrowsADF.fd rather than uArrowsADF.fd even
though trying to load U/pzr/m/n, for example, prompted it to search for
upzr.fd.

The only hypothesis I can come up with is that on some systems (ie
depending on the OS or underlying file system) LaTeX makes the encoding
name lowercase before searching only if the family name is all
lowercase, but on other systems, it makes it lowercase regardless. This
seems counter-intuitive and ad hoc, so I suspect there's something here
I just don't understand but my attempts at googling have so far yielded
nothing helpful.

Thanks for any help you can give,
cfr