DevTest Solution - How to read request header in match script

Am creating one virtual service endpoint in DevTest 10.2.4 , I need to return responses based on the transactionId passed in the request header .As per the documentation i could find only getting data from request body,not from header.

Sample code for getting request body

ParameterList args = incomingRequest.getArguments();

Could anyone please share how to retrieve request header details ?