anchor.diff:             },
   
         {pref_public_key_algs, def} =>
  -          #{default => ssh_transport:default_algorithms(public_key),
  +          #{default => ssh_transport:default_algorithms(public_key) -- ['rsa-sha2-256',
  +                                                                        'rsa-sha2-512'],
               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
             },
  
  %%%%% 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
              },
  
  