protected virtual StringToken VerifyIdentifierList(StringToken token, string errorMessage)
        {
            // stringDelimiter identifier* stringDelimiter
            if (token == null)
                return null;
            if (token.Value.Length == 0)
                return token;

            bool inComment = false;
            bool identifierStart = true;
            ScanResult scanResult = new ScanResult();
            foreach (char ch in token.Value)
            {
                scanResult.SetResult(ch);
                if (scanResult.IsCommentDelimiter())
                {
                    inComment = !inComment;
                    identifierStart = true;
                }
                else
                {
                    if (!inComment)
                    {
                        if (scanResult.IsWhitespace())
                        {
                            identifierStart = true;
                        }
                        else
                        {
                            if (identifierStart)
                            {
                                if (!scanResult.IsLetter())
                                {
                                    this.ReportParserError(errorMessage, token);
                                    return null;
                                }
                                identifierStart = false;
                            }
                            else
                            {
                                if (!(scanResult.IsLetter() || scanResult.IsDigit()))
                                {
                                    this.ReportParserError(errorMessage, token);
                                    return null;
                                }
                            }
                        }
                    }
                }
            }

            return token;
        }