def add(self, tool_cls, widget_cls=None):
        if widget_cls in self.members:
            self.members[widget_cls].append(tool_cls)
        else:
            self.members[widget_cls] = [tool_cls]
Get a subset of the meta data values with the classificaion
dataset/ETHPy150Open glue-viz/glue/glue/config.py/QtToolRegistry.add--crossover with--dataset/ETHPy150Open moloney/dcmstack/src/dcmstack/dcmmeta.py/DcmMetaExtension._global_slice_subset