Is there any difference between rm -r and rm -R?

Title is Description.
I just wonder there is any difference between rm -r and rm -R.

Linux man description is seemed like they are totally same(and one more, --recursive), but many people use -r and -R like they aren't same.

So I want to know about not only its functional difference but its practical(or conventional) difference.
Could anyone let me know about this?

Solution

According to the OpenGroup / POSIX specification for rm, the -r and -R options are equivalent.

Source: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/rm.html

This probably applies to all modern UNIX / Linux variants.

But it wasn't always that way:

The -R option did not exist in v5 UNIX; see here, page 97.
Or in v7 UNIX; see https://www.unix.com/man-page/v7/1/rm/.
It apparently was introduced in 4.2bsd; see https://linuxgazette.net/issue49/fischer.html ... as meaning the same as -r.

The reason for adding -R was for compatibility with other commands that use -R to mean recursive. (For example chmod ... where -r means "remove read permission".)