anchor.diff:  %% directory as for the proto `File'.
   %%
   %% The `{o_erl,directory()}', `{o_hrl,directory()}', `{o_nif_cc,directory()}',
  -%% options specify output directory for where to generate the `.erl'
  +%% options specify output directories for where to generate the `.erl'
   %% and `.hrl' files respectively, and for the NIF C++ file,
   %% if the `nif' option is specified. The `{o_erl,directory()}' option
   %% overrides any `{o,directory()}' option, and similarly for the
  
positive.code: %% messages referencing other messages, when compiling the generated
  %% files. The `type_specs' option is equivalent to `{type_specs,true}'.
  %%
  %% The `verify' option whether or not to generate code for verifying
  %% that, during encoding, values are of correct type and within range.
  %% The `verify' option can have the following values:
  %% <dl>
  %%    <dt>`always'</dt><dd>Generate code that unconditionally
  %%        verifies values.</dd>
  
negative.code: %% in which case they will be proplists instead. This option is not
  %% compatible with the `nif' option.
  %%
  %% The `nif' option will cause the compiler to generate the decoder as
  %% nif C++ code. The generated nif C++ code can be linked with the
  %% Google protobuf C++ library.  Read the file `README.nif-cc' for
  %% more info. This option is not compatible with the `maps' option;
  %% the generated C++ decoding code would still create records.
  %%
  %% The `binary' option will cause the generated and compiled code to be
  %% returned as a binary. No files will be written. The return value
  %% will be on the form `{ok,Mod,Code}' or `{ok,Mod,Code,Warnings}'
  %% if the compilation is succesful. This option may be useful
  