name ::= letter {letter | digit} [id_cont]
  | “_” {“_”} op_name      the first underscore is not part of the msg name
op_name ::= punct {punct} [id_cont]
  | “_” {“_”} name     the first underscore is not part of the msg name

integer ::= [radix] hex_digits      a leading “-” is considered a unary operator
radix ::= digits “_”
hex_digits ::= hex_digit {hex_digit}
hex_digit ::= digit | one of “a..fA..F”
float ::= integer “.” hex_digits [exponent]
  | integer exponent
exponent ::= “^” [ “+“ | “-“] digits
digits ::= digit {digit}

character ::= “ ' ” char “ ' “
string ::= “ " “ { char | line_break } “ " “
char ::= any | “ \ “ escape_char
escape_char ::= one of “ abfnrtv'"\?0 “
  | [“o“| “d” ] digit [digit [digit]]
  | [“o”] digit [digit [digit]]
  | “x“ hex_digit [hex_digit]
line_break ::= “\” {whitespace} new_line {whitespace} “\” nbsp;     characters between \' s are not part of the string
brace_balanced_chars ::= {any but “{“ }
  [ { brace_balanced_chars } {any but “}” }]
letter ::= one of “a..zA..Z”
digit ::= one of “0..9”
punct ::= one of “!#$%^&*-+=<>/?~\|”

whitespace ::= space | tab | newline | comment
comment ::= “--” {any but newline} newline

    | “(--” {any} “--)”;        comment to end of line racketed comment; an be nested