It's great to see a JSON API integrated in Arc. :)
I took a look and found fixes for the unit tests. Before I got into that debugging though, I noticed some problems with the JSON library that I'm not sure what to do with. It turns out those are unrelated to the test failures.
The JSON solution is a quick and dirty hack by a rank noob, and I'm sure something better will come along.
And in hindsight the problem with the (body) macro should probably have been obvious, considering HTML tables are built using (tab) and not (table). I'm starting to think everything other than (tag) should be done away with to avoid the issue in principle, but that would be a major undertaking and probably mostly just bikeshedding.