It looks like this -doc package is just a packaging of a failed Doxygen run, except somehow the .html file didn't even get into it.
The project website seems to have disappeared, though echoes of it live on: http://web.archive.org/web/20090221011519/http://oss.metaparadigm.com/json-c/doc/html/json__object_8h.html -- Duncan Smith -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org