^ matches Beginning of Line
    $ matches End of Line as last character of expression
    \c matches following (hexadecimal value shown in parenthesis):
       \a == bell (alert)    ( \x07 )
       \b == backspace       ( \x08 )
       \f == formfeed        ( \x0c )
       \n == newline         ( \x0a )
       \r == carriage return ( \x0d )
       \s == space           ( \x20 )
       \t == horizontal tab  ( \x09 )
       \v == vertical   tab  ( \x0b )
       \c == c [ \\ == \ ]
       \ooo == character represented by octal value ooo
               1 to 3 octal digits acceptable
       \xhh == character represented by hexadecimal value hh
               1 or 2 hexadecimal digits acceptable

    . matches any character
    [abc0-9] Character Class - match any character in class
    [^abc0-9] Negated Character Class - match any character not in class
    [!abc0-9] Negated Character Class - match any character not in class
    [#abc0-9] Matched Character Class - for second match, class character
              must match in corresponding position
    * - Closure, Zero or more matches
    + - Positive Closure, One or More matches
    ? - Zero or One matches
    r(s)t embedded regular expression s
    r|s|t  '|' == logical 'or' operator. Expression r or s or t

    @ - Look-Ahead, r@t, matches regular expression 'r' only when r  is
        followed  by  regular  expression  't'.    Regular expression t not
        contained  in  final  match.    Symbol  loses  special meaning when
        contained within parenthesis, '()', or character class, '[]'.

    r{n1,n2} - at least n1 and up to n2 repetitions of expression r

         n1, n2 integers with 1 <= n1 <= n2
         r{2,6} ==> rrr?r?r?r?
         r{3,3} ==> rrr
         Expressions grouped by ", (), [], or names, "{name}"
         repeated as a group: (Note the treatment of quoted expressions)
         (r){2,6} ==> (r)(r)(r)?(r)?(r)?(r)?
         [r]{2,6} ==> [r][r][r]?[r]?[r]?[r]?
         {r}{2,6} ==> {r}{r}{r}?{r}?{r}?{r}?
         "r"{2,6} ==> "rr(r)?(r)?(r)?(r)?"

    {named_expr} - named expression.   In regular expressions  "{name}"
    is replaced by the value  of the corresponding variable.   Unrecognized
    variable names are not replaced.  Names starting with an underscore and
    followed  by  a  single  upper  or  lower  case  letter are reserved as
    predefined.  The following predefined names are currently available:

    {_a} == [A-Za-z]                Alphabetic
    {_b} == [{}()[]<>]              Brackets
    {_c} == [\x001-\x01f\x-7f]      Control character
    {_d} == [0-9]                   Digit
    {_e} == [DdEe][-+]?{_d}{1,3}    Exponent
    {_f} == [-+]?({_d}+\.{_d}*|{_d}*\.{_d}+)     Floating point number
    {_g} == {_f}({_e})?             float, optional exponent
    {_h} == [0-9A-Fa-f]             Hex-digit
    {_i} == [-+]?{_d}+              Integer
    {_n} == [A-Za-z0-9]             alpha-Numeric
    {_o} == [0-7]                   Octal digit
    {_p} == [\!-/:-@[-`{-\x07f]     Punctuation
    {_q} == {_s}[\"']               double or single Quote
    {_r} == {_f}{_e}                Real number
    {_s} == (^|[!\\](\\\\)*)        zero or even number of Slashes
    {_t} == [\s-~]                  printable character
    {_u} == [\!-~]                  graphical character
    {_w} == [\s\t]                  White space
    {_z} == [\t-\r\s]               space, \t, \n, \v, \f, \r, \s