The POSIX locale definition says the following:
Define characters to be classified as printable characters, including the <space>. In the POSIX locale, all characters in class graph shall be included; no characters in class cntrl shall be included. In a locale definition file, characters specified for the keywords upper, lower, alpha, digit, xdigit, punct, graph, and the <space> are automatically included in this class. No character specified for the keyword cntrl shall be specified.
So it doesn't explicitly say anything about "space" here, though it doesn't NOT explicitly forbid including "space" in the "print" class, and I *think* we can extend the <space> character being included to the entire "space" character class.