Zend_Json has two different modes depending if ext/json is
enabled in your PHP installation or not. If ext/json is installed by
json_decode() functions are used for encoding and decoding
JSON. If ext/json is not installed a Zend Framework implementation in
PHP code is used for en-/decoding. This is considerably slower than
using the PHP extension, but behaves exactly the same.
Still sometimes you might want to use the internal encoder/decoder even if you have ext/json installed. You can achieve this by calling:
Zend_Json::$useBuiltinEncoderDecoder = true: