If not provided #[0]/Unix command options alphabetically using the man page, use grep (https://www.cyberciti.biz/faq/howto-use-grep-command-in-linux-unix/) to find what a flag does. Here is how to find out what the `-p -m -I -i -M` option does for the rsync:

rsync --help | grep -Ew -- '-(I|i|m|M|p)'

I used simple egrep https://www.cyberciti.biz/faq/grep-regular-expressions/