docs: def add_package(
          self,
          pkg_name,
          recurse=True,
          include_bases=True,
          parent_pkg=None
      ):
          """Add all classes to the backup in the specified package (including
          all modules and all sub-packages) for which is_backup_class returns
          True. Note that self.add_class is used, so base classes will added as
          well.
  
          Parameters:
          * pkg_name - a string representing the package name. It may be
            relative _if_ parent_pkg is supplied as well
          * recurse - (default value of True) if False, sub-packages will _not_
            be examined
          * include_bases - (default value of True) is passed directly to
            add_class for every class added
          * parent_pkg - a string representing the parent package of the relative
            package specified in pkg_name. Note that you should specify
            parent_pkg _only_ if pkg_name should be interpreted as relative
  
          An an example of both relative and absolute package imports, these
          are equivalent:
  
          ````
          backup.add_package('toppackage.subpackage')
          backup.add_package('subpackage', parent_pkg='toppackage')
          ````
          """
          if parent_pkg:
              pkg = import_module('.' + pkg_name, parent_pkg)
          else:
              pkg = import_module(pkg_name)
  
          for module_loader, name, ispkg in pkgutil.walk_packages(pkg.__path__):
              if not ispkg:
                  # Module
                  mod = import_module('.' + name, pkg_name)
                  for name, member in getmembers(mod):
                      if is_backup_class(member):
                          self.add_class(member, include_bases=include_bases)
              elif recurse:
                  # Package and we're supposed to recurse
                  self.add_package(
                      pkg_name + '.' + name,
                      recurse=True,
                      include_bases=include_bases,
                      parent_pkg=parent_pkg
                  )