-where <version> is the numeric version; currently 24. It follows this
-with a free text message-of-the-day. It expects to see a similar
-greeting back from the client.
+where <version> is the numeric version (see PROTOCOL_VERSION in rsync.h)
+'.' is a literal period, and <subprotocol> is the numeric subprotocol
+version (see SUBPROTOCOL_VERSION -- it will be 0 for final releases).
+Protocols prior to 30 only output <version> alone. The daemon expects
+to see a similar greeting back from the client. For protocols prior to
+30, an absent ".<subprotocol>" value is assumed to be 0. For protocol
+30, an absent value is a fatal error. The daemon then follows this line
+with a free-format text message-of-the-day (if any is defined).