I send data from javascript to PHP like this:
$.ajax({'url': 'my.php',
        'type': 'POST',
        'data': JSON.stringify(update_data),
        'success': function(response) {
                       alert(response);
                   }
       });
Using HTTPFOX Firefox plug-in I see the following data in the POST DATA tab:
{"file_id":["1","2","3"],"description":["lala","kuku","wow!"],"tags":[["julia","paper"],["Very nice car"],[]]}
however, if I do in my.php print_r($_POST) I see an empty array. Why is that ? How could I collect the data ?