The following equivalences to Unicode \p{} constructs and equivalent
    backslash character classes (if available), will hold:

        [:...:]     \p{...}         backslash

        alpha       IsAlpha
        alnum       IsAlnum
        ascii       IsASCII
        blank       IsSpace
        cntrl       IsCntrl
        digit       IsDigit        \d
        graph       IsGraph
        lower       IsLower
        print       IsPrint
        punct       IsPunct
        space       IsSpace
                    IsSpacePerl    \s
        upper       IsUpper
        word        IsWord
        xdigit      IsXDigit

    <em>For example "[:lower:]" and "\p{IsLower}" are equivalent.</em>