/// <summary>
/// Starts a transaction under which all undo redo operations take place
/// </summary>
/// <param name="tran"></param>
public void StartTransaction(UndoTransaction tran)
{
if (_curTran == null)
{
_curTran = tran;
///push an empty undo operation
_undoStack.Push(new UndoTransaction(tran.Name));
_redoStack.Push(new UndoTransaction(tran.Name));
}
}