Mono.CSharp.CommandLineParser.IsExternAliasValid C# (CSharp) Method

        static bool IsExternAliasValid(string identifier)
        {
            if (identifier.Length == 0)
                return false;
            if (identifier[0] != '_' && !char.IsLetter (identifier[0]))
                return false;

            for (int i = 1; i < identifier.Length; i++) {
                char c = identifier[i];
                if (char.IsLetter (c) || char.IsDigit (c))
                    continue;

                UnicodeCategory category = char.GetUnicodeCategory (c);
                if (category != UnicodeCategory.Format || category != UnicodeCategory.NonSpacingMark ||
                        category != UnicodeCategory.SpacingCombiningMark ||
                        category != UnicodeCategory.ConnectorPunctuation)
                    return false;
            }

            return true;
        }