A set of stacked plots is a PlotPage. Originally the time window (begin and end times) was an attribute of the PlotPage since the same begin and end times are shared by all the stacked plots. Conceptually, that's where the user associates the time range being plotted, with the whole "page of plots". However, the PlotWindow now owns the DataDomain, and that same domain is shared by all of its plot pages and their plots.