docs: def env(self):
          """The execution context for rowprocessors and row-generating notebooks and functions. """
          from copy import copy
  
          env = copy(self.doc.env)
  
          assert env is not None, 'Got a null execution context'
  
          env.update(self._envvar_env)
  
          env.update(self.all_props)
  
          return env