POSIX.1 is clear - a regular file is a sequence of bytes and that is the only requirement.   See my previous email where I give the section number which is very crisp. 

Sent from a handheld expect more typos than usual

On Thu, Mar 27, 2025 at 8:19 PM Rob Pike <robpike@gmail.com> wrote:

What is a "character" according to POSIX? I suspect it's just a byte, which is a long-outdated definition, the char keyword notwithstanding.

-rob