System.Text.RegularExpressions.RegexCharClass.AddRange C# (CSharp) Method

        internal void AddRange(char first, char last) {
            _rangelist.Add(new SingleRange(first, last));
            if (_canonical && _rangelist.Count > 0 &&
                first <= ((SingleRange)_rangelist[_rangelist.Count - 1])._last) {
                _canonical = false;
            }
        }

        internal RegexFC(char ch, bool not, bool nullable, bool caseInsensitive)
        {
            _cc = new RegexCharClass();

            if (not)
            {
                if (ch > 0)
                    _cc.AddRange('\0', (char)(ch - 1));
                if (ch < 0xFFFF)
                    _cc.AddRange((char)(ch + 1), '\uFFFF');
            }
            else
            {
                _cc.AddRange(ch, ch);
            }

            _caseInsensitive = caseInsensitive;
            _nullable = nullable;
        }