System.Text.RegularExpressions.RegexParser.ScanCharEscape C# (CSharp) Method

        internal char ScanCharEscape()
        {
            char ch;

            ch = MoveRightGetChar();

            if (ch >= '0' && ch <= '7')
            {
                MoveLeft();
                return ScanOctal();
            }

            switch (ch)
            {
                case 'x':
                    return ScanHex(2);
                case 'u':
                    return ScanHex(4);
                case 'a':
                    return '\u0007';
                case 'b':
                    return '\b';
                case 'e':
                    return '\u001B';
                case 'f':
                    return '\f';
                case 'n':
                    return '\n';
                case 'r':
                    return '\r';
                case 't':
                    return '\t';
                case 'v':
                    return '\u000B';
                case 'c':
                    return ScanControl();
                default:
                    if (!UseOptionE() && RegexCharClass.IsWordChar(ch))
                        throw MakeException(SR.Format(SR.UnrecognizedEscape, ch.ToString()));
                    return ch;
            }
        }

 internal static string Unescape(string input)
 {
     for (int i = 0; i < input.Length; i++)
     {
         if (input[i] == '\\')
         {
             StringBuilder builder = new StringBuilder();
             RegexParser parser = new RegexParser(CultureInfo.InvariantCulture);
             parser.SetPattern(input);
             builder.Append(input, 0, i);
             do
             {
                 i++;
                 parser.Textto(i);
                 if (i < input.Length)
                 {
                     builder.Append(parser.ScanCharEscape());
                 }
                 i = parser.Textpos();
                 int startIndex = i;
                 while ((i < input.Length) && (input[i] != '\\'))
                 {
                     i++;
                 }
                 builder.Append(input, startIndex, i - startIndex);
             }
             while (i < input.Length);
             return builder.ToString();
         }
     }
     return input;
 }