docs: def new_child(self):
          """Get a new child :class:`Environment`.
  
          The child's scopes will be mine, with an additional empty innermost
          one.
  
          Returns:
              Environment: The child.
          """
          child = Environment(self.globals, self.max_things)
          child.scopes = self.scopes.new_child()
          child.things = WeakSet(self.things)
          return child