SAP Idoc serialization

I am using WebMethods Enterprise 4.1.1 and the ALE Server adapter to process Idoc�s coming from SAP. How can I make sure that when sending multiple Idoc�s, they get processed in the correct order, meaning that one message doesn�t overtake the other when going from SAP to the broker or when the message is being processed? On the SAP side there is serialization that allows the Idoc�s to be placed in the correct order, if that order was changed during transmission.
The enterprise server documentation talks about sequence numbers as well, but then more in the context of making sure that a message is not processed twice, if I understand correctly. Any suggestions on how to use the SAP serialization number to make sure the Idoc�s get processed in the correct order? Or any other way besides the SAP serialization number?