Html401IdUtil

// Valid IDs are defined in http://www.w3.org/TR/html401/types.html#type-id
        private static class Html401IdUtil {
            private static bool IsAllowableSpecialCharacter(char c) {
                switch (c) {
                    case '-':
                    case '_':
                    case ':':
                        // note that we're specifically excluding the '.' character
                        return true;

                    default:
                        return false;
                }
            }

            private static bool IsDigit(char c) {
                return ('0' <= c && c <= '9');
            }

            public static bool IsLetter(char c) {
                return (('A' <= c && c <= 'Z') || ('a' <= c && c <= 'z'));
            }

            public static bool IsValidIdCharacter(char c) {
                return (IsLetter(c) || IsDigit(c) || IsAllowableSpecialCharacter(c));
            }
        }