docs: def check_m(pm):
      '''
      Shared helper function for all :ref:`tools` to check if the passed
      m-function is indeed :func:`photon.Photon.m`
  
      :params pm:
          Suspected m-function
      :returns:
          Now to be proven correct m-function,
          tears down whole application otherwise.
      '''
  
      if not any([
          callable(pm),
          pm.__name__ != Photon.m.__name__,
          pm.__doc__ != Photon.m.__doc__
      ]):
          shell_notify(
              'wrong "m-function" passed!',
              state=True,
              more=pm.__name__
          )
      return pm