def keys(self, iotype=None, flatten=False):
        return [k for k, v in self.items(iotype, flatten=flatten)]
Check whether all matched elements are visible.
dataset/ETHPy150Open OpenMDAO/OpenMDAO-Framework/openmdao.main/src/openmdao/main/case.py/Case.keys--crossover with--dataset/ETHPy150Open edx/bok-choy/bok_choy/query.py/BrowserQuery.visible