Discussion with the core developers has shown that there are more people 
opposed to including a JSON option printer than people in favor of this change. 
Therefore, I'm closing this issue. 

Just for future reference, I'll note an interesting use-case for the feature at 
hand, that we found after the discusion: Running SMAC on the generated Fast 
Downward parameter files for very short timeouts yields an easy way of testing 
the planner on a wide range of configurations. A first quick test of this 
method allowed us to find and fix four bugs in the planner.

Sounds good.

The other DocPrinter subclasses do their work in the methods print_usage(), 
print_notes(), print_properties(), etc., whereas JsonPrinter only uses 
print_usage(). I think I'll make this more uniform and split up the json export 
into the print_notes(), print_properties(), etc. methods.

No strong opinion on --txt2tags/--json vs. --format {...}.

I'm not sure I understand the other question. Is it about whether that stuff
should be included in the JSON output? If it's not too much work, I would say
that the JSON output should be as complete as possible.

I'll investigate the licensing issue and write to downward-dev. What about the 
two questions in the pull request?

Should we add the documentation parts in the respective DocPrinter methods 
(print_notes(), print_properties(), etc.)?

Should we remove the --txt2tags and --json flags in favor of a "--format 
{json,txt2tags}" commandline option?

Adding is a dependency is something we need to discuss with downward-dev, I
would say. If we can honour the license by sticking the necessary files into a
separate directory and if it doesn't complicate the build, I have no major
objections.

The current patch looks good to me, though it's not fully clear to me if it
honours Jzon's license. Are you certain that this is enough? If not, perhaps
contact the author.

Writing basic SMAC parameter files was indeed possible from within Fast Downward, 
but the final strategy I chose is to output the documentation in JSON format and 
use a python script to convert the JSON output into the SMAC parameter file 
format. 

I think it would be nice to integrate the patch into the master repository. 
Otherwise it may fall prey to bitrot and subsequent work that wants to use the 
SMAC parameter generator will be less easy to conduct. The patch is not very 
intrusive, but it adds the dependency to JZon (https://github.com/Zguy/Jzon) a 
simple and lightweight JSON writer (and parser).

The code is at https://bitbucket.org/jendrikseipp/downward/pull-request/32
I'm attaching a sample output for "./downward-debug --help --json ff".
What do you think?

I'd like to see if we can let the planner (probably only the search component) 
write basic SMAC parameter files or at least parts of them.