+&h3(Multi-threaded Calling)
+The support for an application to issue a &ital(blocking call) by the &cw(rmr_call()) function
+was limited such that only user applications which were operating in a single thread
+could safely use the function.
+Further, timeouts were message count based and not time unit based.
+Multi-threaded call support adds the ability for a user application with multiple threads
+to invoke a blocking call function with the guarantee that the correct response message
+is delivered to the thread.
+The additional support is implemented with the &ital(rmr_mt_call()) and &ital(rmr_mt_rcv())
+function calls.
+&space
+
+Multi-threaded call support requires the user application to specifically enable it
+when RMR is initialised.
+This is necessary because a second, dedicated, receiver thread must be started, and
+requires all messages to be examined and queued by this thread.
+The additional overhead is minimal, queuing information is all in the RMR message
+header, but as an additional process is necessary the user application must "opt in"
+to this approach.
+
+&space
+&h2(ENVIRONMENT)
+As a part of the initialisation process &cw(rmr_init) reads
+environment variables to configure itself.
+The following variables are used if found.
+&half_space
+
+.** the list of environment vars supported
+.im &{lib}/man/env_var_list.im
+