5 POSIX specification:@* @url{https://pubs.opengroup.org/onlinepubs/9699919799/functions/isatty.html}
9 Portability problems fixed by Gnulib:
12 On native Windows, this function also returns true for character devices such
15 On native Windows, this function returns false for Cygwin consoles.
17 This function crashes when invoked with invalid arguments on some platforms:
21 Portability problems not fixed by Gnulib: