anchor.diff:  
   -type filename() :: file:filename().
   -type proplist() :: proplists:proplist().
  +-type context() :: module | footer | function | overview | single.
   
   %% @doc Like {@link source/5}, but reads the syntax tree and the
   %% comments from the specified file.
  
positive.code: 
  -spec file(File, Context, Env, Opts) -> {ok, Tags} | {error, Reason} when
        File :: filename(),
        Context :: edoc_tags:tag_flag(),
        Env :: edoc:env(),
        Opts :: proplist(),
        Tags :: [term()],
  
negative.code: 
  -spec text(Text, Context, Env, Opts) -> Tags when
        Text :: string(),
        Context :: context(),
        Env :: edoc:env(),
        Opts :: proplist(),
        Tags :: [term()].
  