System.ComponentModel.MaskedTextProvider.ResetChar C# (CSharp) Method

        private void ResetChar(int testPosition)
        {
            CharDescriptor chDex = _stringDescriptor[testPosition];

            if (IsEditPosition(testPosition) && chDex.IsAssigned)
            {
                chDex.IsAssigned = false;
                _testString[testPosition] = _promptChar;
                _assignedCharCount--;

                if (chDex.CharType == CharType.EditRequired)
                {
                    _requiredCharCount--;
                }

                Debug.Assert(_assignedCharCount >= 0, "Invalid count of assigned chars.");
            }
        }