docs: def MetaField(self, name, t=None):
          """
          Creates an instance of a metadata field of the dataset. It can be used in building expressions
          or conditions for projection or selection.
          Notice that this function is equivalent to call::
              
              dataset["name"]
  
          If the MetaField is used in a region projection (:meth:`~.reg_project`), the user has also to specify the type
          of the metadata attribute that is selected::
  
              dataset.reg_project(new_field_dict={'new_field': dataset['name', 'string']})
  
          :param name: the name of the metadata that is considered
          :param t: the type of the metadata attribute {string, int, boolean, double}
  
          :return: a MetaField instance
          """
          return MetaField(name=name, index=self.__index, t=t)