private void ResetString(int startPosition, int endPosition)
{
Debug.Assert(startPosition >= 0 && endPosition >= 0 && endPosition >= startPosition && endPosition < _testString.Length, "position out of range.");
startPosition = FindAssignedEditPositionFrom(startPosition, forward);
if (startPosition != invalidIndex)
{
endPosition = FindAssignedEditPositionFrom(endPosition, backward);
while (startPosition <= endPosition)
{
startPosition = FindAssignedEditPositionFrom(startPosition, forward);
ResetChar(startPosition);
startPosition++;
}
}
}