For those of you who wants to use JSON with PHP4 to process russian KOI8-r text, please read the following article: http://yozhek10nozhek.livejournal.com/5842.html (in russian)
Maybe it is neither completed yet nor professionally-written, but it doesn't aim to be some kind of full-featured manual.
Note, that you must have iconv extension loaded to use it; json extension is not needed, I use Services_JSON (http://pear.php.net/pepr/pepr-proposal-show.php?id=198) implementation.
LXX. JSON Functions
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The JSON function is basically a more widely accepted variation on the WDDX principle:
giunta dot gaetano at sea-aeroportimilano dot it
Two pure-php implementations of the json protocol that might be of use, e.g. for php 4 installs where adding extensions is not an option or because of extra functionality can be found here:
http://sourceforge.net/projects/phpxmlrpc (look for the extras package)
Of course, performance is abysmal compared to the php extension, written in highly optimized C code...