A character counts as white space if it satisfies code_type(Code, space), i.e., the C library function iswspace(). This depends on the locale. Using a Unicode locale this includes the Unicode separator characters such as \u00a0 (no-break space) and \u3000 (ideographic space), while in the C locale only the ASCII white space characters are recognised. Note that the bidi format characters \u200e and \u200f are not white space and are thus preserved.