def METHOD_NAME(self, chunk, fields):
    """Not implemented yet."""
    # This reads the data from a single chunk without doing any selection,
    # and is only used for caching data that might be used by multiple
    # different selectors later. For instance, this can speed up ghost zone
    # computation.
    # it should be used by _read_fluid_selection instead of _read_data
    raise NotImplementedError