anchor.diff:  -type chunk_summary() :: {file_offset(), chunk_size(), chunk_bin(), chunk_cstrm()}.
   -type chunk_pos()   :: {file_offset(), chunk_size(), file_name_s()}.
   -type chunk_size()  :: non_neg_integer().
  +
  +%% Tags that stand for how that checksum was generated. See
  +%% machi_util:make_tagged_csum/{1,2} for further documentation and
  +%% implementation.
  +-type csum_tag()    :: none | client_sha | server_sha | server_regen_sha.
  +
   -type error_general() :: 'bad_arg' | 'wedged' | 'bad_checksum'.
   -type epoch_csum()  :: binary().
   -type epoch_num()   :: -1 | non_neg_integer().
  
positive.code:               chunk_summary/0,
                chunk_pos/0,
                chunk_size/0,
                error_general/0,
                epoch_csum/0,
                epoch_num/0,
  
negative.code: -type read_opts()   :: #read_opts{}.
  -type read_opts_x() :: 'undefined' | 'noopt' | 'none' | #read_opts{}.
  
  -export_type([
                append_opts/0,
                chunk/0,
  