Document long options's behaviour (such as --rcfile) when there are no =
It seems to me that although not documented, yash --rcfile foo.sh seems to work. The form without the equal sign is very handy when one starts the shell in C (for example, execl("/bin/yash", "yash", "--rcfile", somefile)). It would be nice if this behaviour is documented or shown in the --help page.
It's documented in: https://yash.osdn.jp/doc/builtin.html#argsyntax
The rule for the equal sign is so universal that it may be too verbose to mention the rule in every description of a long option...