anchor.diff:  after_nl([${,$\n|T], Env, L, Doc)  -> pre(T, Env, L, Doc);
   after_nl([${,${|T], Env, L, Doc)   -> emb(T, Env, L, Doc);
   after_nl([${|T], Env, L, Doc)      -> pre(T, Env, L, Doc);
  +after_nl("[expires:"++T, Env, L, Doc) -> eregion(T, Env, L, Doc);
   after_nl([$[|T], Env, L, Doc)      -> note(T, Env, L, Doc);
   after_nl("____" ++ T, Env, L, Doc) -> hr(T, Env, L, Doc);
   after_nl(S=[$-|T], Env, L, Doc)    -> mk_list(S, Env, L, Doc);
  
positive.code:     emb(T, Env, [H|L], Doc);
  emb([], Env, L, Doc) ->
      emb([$},$}], Env, L, Doc).
  
  note(T, Env, L, Doc) ->
      {Env1, L1} = clear_line(Env, L),
  
negative.code: %%
  %% Blocks (denoted by special characters in column 1):
  %%                      [              Note
  %%                        ...
  %%                      ]
  %%                      [expires:Date  expire tagged region
  %%                        ...
  %%                      ]
  %%                      {              Preformatted
  