>>> - (or (char-after (point)) :json-eof))
>> I wonder why it used :json-eof instead of using nil ?
>> Any idea?
> Not sure--it has been there since json.el was added to Emacs.
Then why use 0 now instead of nil?
Because `following-char' returns 0 at EOB. "At the end of the buffer or accessible region, return 0."