def getPropertyDataSource(self):
        raise NotImplementedError
Sets the downHovering face of the button.
dataset/ETHPy150Open rwl/muntjac/muntjac/data/property.py/IViewer.getPropertyDataSource--crossover with--dataset/ETHPy150Open anandology/pyjamas/library/pyjamas/ui/CustomButton.py/CustomButton.setDownHoveringFace