The contents of the message tree are updated if an exception is raised.
If no exception occurs while processing the message, the tree structure and content received by an individual node is determined by the action of previous nodes in the flow.
If an exception occurs in the message flow, the content of the four trees depends on the following factors:
Exception handling paths start at a failure terminal (most message processing nodes have these), the catch terminal of an input node, a TryCatch node, or an AggregateReply node, but are no different in principle from a normal message flow path. Such a flow consists of a sequence of nodes connected together by the designer of the message flow. The exception handling paths differ in the kind of processing that they do to record or react to the exception. For example, they might examine the exception list to determine the nature of the error, and take appropriate action or log data from the message or exception.
The LocalEnvironment and message tree that are propagated to the exception handling message flow path are those at the start of the exception path, not those at the point when the exception is thrown. The figure below illustrates this point: