From a (quick) look at it, I think tidy is return the information in serialized format, so you need to do this:
$str = get_tidy_data(); // or whatever you do...
$results = unserialize($str);
It seems that the unserialzed object will be a numerically-indexed array with two elements. Once you've unserialized the data, you can take a quick look with
The PHP manual page for unserialize is here: http://us3.php.net/manual/en/function.unserialize.php
As for traversal, well, at that point it's like traversing any array in PHP.
The JSON page is here http://json.org/