+RMR interactions are processed in a thread started by the framework.
+This implementation detail is documented here for transparency, but
+most users will not have to worry about this.
+
+In both types of Xapp, the framework launches a separate thread whose
+only job is to read from RMR and deposit all messages (and their
+summaries) into a thread-safe queue. When the client Xapp reads from
+RMR using the framework (this read is done by the framework itself in
+the RMR Xapp, but by the client in a general Xapp), the read is done
+from the framework-managed queue. The framework is implemented this
+way so that a long-running client function (e.g., consume) will not
+block RMR reads. This is important because RMR is *not* a persistent
+message bus; if an RMR client does not read fast enough, messages can
+be lost. So in this framework the client code is not in the same
+thread as the RMR reads, to ensure that long-running client code will
+not cause message loss.
+
+In the case of RMR Xapps, there are currently 3 potential threads; the
+thread that reads from RMR directly, and the user can optionally have
+the RMR queue read run in a thread, returning execution back to the
+user thread. The default is only two threads however, where `.run`
+does not return back execution and the user code is finished at that
+point.
+
+Healthchecks
+------------
+
+The framework provides a default RMR healthcheck probe handler for
+reactive Xapps. When an RMR healthcheck message arrives, this handler
+checks that the RMR thread is healthy (of course the Xapp cannot even
+reply if the thread is not healthy!), and that the SDL connection is
+healthy. The handler responds accordingly via RMR. The Xapp can
+override this probe handler by registering a new callback for the
+healthcheck message type.
+
+The framework provides no healthcheck handler for general Xapps. Those
+applications must handle healthcheck probe messages appropriately when
+they read their RMR mailboxes.
+
+There is no http service in the framework, so there is no support for
+HTTP-based healthcheck probes, such as what a deployment manager like
+Kubernetes may use.