The GNU standard for --version and --help says the program should write to standard output and exit with success. Cf., https://www.gnu.org/prep/standards/html_node/_002d_002dhelp.html#g_t_002d_002dhelp
What happens with an illegal option that the program rejects and exits? Does the message get written to standard output or standard error? Should the program exit with an error? (I'm fairly certain it should exit with an error, but I can't tell where the message should be printed). If the information could be added to https://www.gnu.org/prep/standards/html_node/Command_002dLine-Interfaces.html, then it would be greatly appreciated. Jeffrey Walton Baltimore, MD, US
