void PreviousVersion()
{
EnsureSaved();
if (_currentPage >= Book.Pages.Count)
{
return;
}
if (_currentIterator == null)
{
_currentIterator = Book.Pages[_currentPage].GetIterator();
_currentIterator.MoveToEnd();
}
if (_currentIterator.MovePrevious())
{
UpdateTextBox();
UpdateViewLabels();
}
}