Convenience API for accessing headers attached to the message.
Unmodified message as received by the Solace message broker.
Contains the resolved values of named single-level wildcard segments as specified in the topic.
For example: If subscribed to the topic person/:id and a message is published to the topic person/5,
the resolved id with the value 5 is contained in the segments map.
Envelope containing the Message and resolved values for named topic segments, if any.