[boost] [Boost.Filesystem] unique_path uses a random number generator from the OS, correct?

The reference docs for unique_path state: Remarks: Implementations are encouraged to obtain the required randomness via a cryptographically secure pseudo-random number generator, such as one provided by the operating system. I'm confused by the "implementations are encouraged to" text. Isn't Boost.Filesystem the implementation of unique_path? Specifically, it *looks like* this is provided in unique_path.cpp which will use either CryptGenRandom from the Windows API; or /dev/urandom or /dev/random on POSIX systems. This means the random number comes from system/OS utilities, and not Boost itself, correct? -- Ben Fritz