Taking this parameter by const reference forces us to copy it (because
we know we're going to store it). Taking it by r-value reference would
suggest that we _might_ take ownership over it and would also force the
user to make a copy if they wish to retain the original value.
Taking this parameter by value however clearly gives us ownership of its
content without forcing a copy if it's implicit conversion from
`const char*` or explicitly handed over to us by the user via std::move.