The iswblank function tests for any wide character that is a standard
    blank wide character or is one of a locale-specific set of wide
    characters for which iswspace is true and that is used to separate
    words within a line of text.

    The standard blank wide characters are the space character (L' ') and
    horizontal tab character (L'\t').

    In the "C" locale, iswblank returns true only for the standard blank
    characters.

    See also isblank.