docs: def data_spec(cls, name):
          """
          Return the fileset_spec, i.e. the template of the fileset expected to
          be supplied or generated corresponding to the fileset_spec name.
  
          Parameters
          ----------
          name : Str
              Name of the fileset_spec to return
          """
          # If the provided "name" is actually a data item or parameter then
          # replace it with its name.
          if isinstance(name, BaseData):
              name = name.name
          try:
              return cls._data_specs[name]
          except KeyError:
              raise ArcanaNameError(
                  name,
                  "No fileset spec named '{}' in {}, available:\n{}"
                  .format(name, cls.__name__,
                          "\n".join(list(cls._data_specs.keys()))))