Warning:
    Modifying inputs or outputs inplace is not allowed when using
    backward hooks and will raise an error.

  Parameters:
     * **hook** (*Callable*) -- The user-defined hook to be
       registered.

     * **prepend** (*bool*) -- If true, the provided "hook" will
       be fired before all existing "backward" hooks on this
       "torch.nn.modules.Module". Otherwise, the provided "hook"
       will be fired after all existing "backward" hooks on this
       "torch.nn.modules.Module". Note that global "backward"
       hooks registered with
       "register_module_full_backward_hook()" will fire before all
       hooks registered by this method.

  Returns:
     a handle that can be used to remove the added hook by calling
     "handle.remove()"

  Return type:
     "torch.utils.hooks.RemovableHandle"

register_full_backward_pre_hook(hook, prepend=False)
  Registers a backward pre-hook on the module.
