JOpera for Eclipse

Dear JOpera team,
what are the standard means to trigger events on JOpera sessions and how are these used ? I'd like to design the application in a reactive way to trigger processing by internal / external events. The MSG adapter seems most appropriate, but there is no documentation supplied [1]. After study of examples (msg_example*.oml) it seems, that message queues are shared between processes to exchange echo-style variables. Could a message be passed from outside (REST) at any point of processing to a specific process instance ?

Thank you
Jaro

[1] http://www.jopera.org/docs/help/jop_14.html#sec_ref_MSG