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

        internal RegexNode ScanDollar()
        {
            if (CharsRight() == 0)
                return new RegexNode(RegexNode.One, _options, '$');

            char ch = RightChar();
            bool angled;
            int backpos = Textpos();
            int lastEndPos = backpos;

            // Note angle

            if (ch == '{' && CharsRight() > 1)
            {
                angled = true;
                MoveRight();
                ch = RightChar();
            }
            else
            {
                angled = false;
            }

            // Try to parse backreference: \1 or \{1} or \{cap}

            if (ch >= '0' && ch <= '9')
            {
                if (!angled && UseOptionE())
                {
                    int capnum = -1;
                    int newcapnum = (int)(ch - '0');
                    MoveRight();
                    if (IsCaptureSlot(newcapnum))
                    {
                        capnum = newcapnum;
                        lastEndPos = Textpos();
                    }

                    while (CharsRight() > 0 && (ch = RightChar()) >= '0' && ch <= '9')
                    {
                        int digit = (int)(ch - '0');
                        if (newcapnum > (MaxValueDiv10) || (newcapnum == (MaxValueDiv10) && digit > (MaxValueMod10)))
                            throw MakeException(SR.CaptureGroupOutOfRange);

                        newcapnum = newcapnum * 10 + digit;

                        MoveRight();
                        if (IsCaptureSlot(newcapnum))
                        {
                            capnum = newcapnum;
                            lastEndPos = Textpos();
                        }
                    }
                    Textto(lastEndPos);
                    if (capnum >= 0)
                        return new RegexNode(RegexNode.Ref, _options, capnum);
                }
                else
                {
                    int capnum = ScanDecimal();
                    if (!angled || CharsRight() > 0 && MoveRightGetChar() == '}')
                    {
                        if (IsCaptureSlot(capnum))
                            return new RegexNode(RegexNode.Ref, _options, capnum);
                    }
                }
            }
            else if (angled && RegexCharClass.IsWordChar(ch))
            {
                string capname = ScanCapname();

                if (CharsRight() > 0 && MoveRightGetChar() == '}')
                {
                    if (IsCaptureName(capname))
                        return new RegexNode(RegexNode.Ref, _options, CaptureSlotFromName(capname));
                }
            }
            else if (!angled)
            {
                int capnum = 1;

                switch (ch)
                {
                    case '$':
                        MoveRight();
                        return new RegexNode(RegexNode.One, _options, '$');

                    case '&':
                        capnum = 0;
                        break;

                    case '`':
                        capnum = RegexReplacement.LeftPortion;
                        break;

                    case '\'':
                        capnum = RegexReplacement.RightPortion;
                        break;

                    case '+':
                        capnum = RegexReplacement.LastGroup;
                        break;

                    case '_':
                        capnum = RegexReplacement.WholeString;
                        break;
                }

                if (capnum != 1)
                {
                    MoveRight();
                    return new RegexNode(RegexNode.Ref, _options, capnum);
                }
            }

            // unrecognized $: literalize

            Textto(backpos);
            return new RegexNode(RegexNode.One, _options, '$');
        }