the content to send to the server. By default, it is encoded into several parameters and the data parameters (data_*) is encoded in JSON.
If you prefer to encode it into another format, you could override this method, and also implement a Java interface called org.zkoss.zk.au.AuDecoder to decode the format at the server.
If you prefer to encode it into URI, you could override beforeSend.
5.0.4
the order of the AU request. ZK sends a batch of AU request at once and this argument indicates the order an AU request is (starting from 0).