c:ext. What the model does not read of an extension is kept in its Element.unknown.
c:ext
Optional
c15:datalabelsRange: the cells a series' data labels show (Excel's "Value From Cells").
c15:datalabelsRange
c15:showDataLabelsRange, on a series' labels: whether they show those cells.
c15:showDataLabelsRange
c:ext. What the model does not read of an extension is kept in its Element.unknown.