anchor.diff:             },
   
         {pref_public_key_algs, def} =>
  -          #{default => ssh_transport:default_algorithms(public_key) -- ['rsa-sha2-256',
  -                                                                        'rsa-sha2-512'],
  +          #{default => ssh_transport:default_algorithms(public_key),
               chk => fun check_pref_public_key_algs/1,
  -            class => user_options
  -           },
  -
  -      {preferred_algorithms, def} =>
  -          #{default => [{K,Vs} || {K,Vs0} <- ssh:default_algorithms(),
  -                                  Vs <- [case K of
  -                                             public_key -> 
  -                                                 Vs0 -- ['rsa-sha2-256',
  -                                                         'rsa-sha2-512'];
  -                                             _ ->
  -                                                 Vs0
  -                                         end]
  -                       ],
  -            chk => fun check_preferred_algorithms/1,
               class => user_options
              },
   
  
positive.code:             class => user_options
             },
  
        {preferred_algorithms, def} =>
            #{default => ssh:default_algorithms(),
              chk => fun check_preferred_algorithms/1,
              class => user_options
             },
  
  %%%%% Undocumented
        {infofun, def} =>
            #{default => fun(_,_,_) -> void end,
  
negative.code:        {user_dir, def} =>
             #{default => false, % FIXME: TBD ~/.ssh at time of call when user is known
               chk => fun(V) -> check_string(V) andalso check_dir(V) end,
               class => user_options
              },
  
         {preferred_algorithms, def} =>
             #{default => ssh:default_algorithms(),
               chk => fun check_preferred_algorithms/1,
               class => user_options
              },
  
  