When a message is sent and the data is consumed, the HL7 protocol requires that the receiver send back a valid HL7 ACKnowledgment message. Setting up ACKnowledgment messages can be an annoying detail of HL7. It is desirable to be able to alter the format of ACK messages on the fly without needing to alter your application's source code (in the case of Chameleon). With Iguana, the format of ACK messages can be customized by editing the message definition file (VMD).

With Chameleon, Python scripts are used to automatically extract the required fields from an incoming message, and then populate an ACK message with this data on the outgoing side. This technique is used by iNTERFACEWARE tools like Iguana and the HL7 Listener. The same technique can also be used by customers in their own custom implementations using Chameleon.