private string ProcessClosed(string bounder)
        {
            foreach (var expresson in _registeredExpressions)
            {
                if (expresson.LeftBounder == bounder)
                {
                    openedBy = expresson;
                    return string.Empty;
                }

                if (expresson.LeftBounder.StartsWith(bounder))
                {
                    return bounder;
                }
            }

            return string.Empty;
        }
        private string ProcessOpened(string bounder)
        {
            if (openedBy.RightBounder == bounder)
            {
                openedBy = null;
                return string.Empty;
            }

            if (openedBy.RightBounder.StartsWith(bounder))
            {
                return bounder;
            }

            return string.Empty;
        }