Index special characters in IDL Syntax

% -> mult_expr
( -> context_expr
            -> parameter_dcls
            -> primary_expr
            -> raises_expr
            -> union_type
) -> context_expr
            -> parameter_dcls
            -> primary_expr
            -> raises_expr
            -> union_type
* -> mult_expr
+ -> add_expr
            -> unary_operator
, -> attr_dcl
            -> context_expr
            -> declarators
            -> enum_type
            -> inheritance_spec
            -> parameter_dcls
            -> raises_expr
            -> sequence_type
- -> add_expr
            -> unary_operator
/ -> mult_expr
:: -> scoped_name
: -> case_label
            -> inheritance_spec
; -> case
            -> definition
            -> export
            -> member
~ -> unary_operator
^ -> xor_expr
< -> sequence_type
            -> string_type
<< -> shift_expr
= -> const_dcl
> -> sequence_type
            -> string_type
>> -> shift_expr
& -> and_expr