📚 Document NOOP command (allow EXPUNGE data)

Author: nevans

lib/net/imap.rb

@@ -518,6 +518,16 @@ def id(client_id=nil)
     # Sends a {NOOP command [IMAP4rev1
     # §6.1.2]}[https://www.rfc-editor.org/rfc/rfc3501#section-6.1.2] to the
     # server.
+    #
+    # This allows the server to send unsolicited untagged EXPUNGE #responses,
+    # but does not execute any client request.  \IMAP servers are permitted to
+    # send unsolicited untagged responses at any time, except for `EXPUNGE`.
+    #
+    # * +EXPUNGE+ can only be sent while a command is in progress.
+    # * +EXPUNGE+ must _not_ be sent during #fetch, #store, or #search.
+    # * +EXPUNGE+ may be sent during #uid_fetch, #uid_store, or #uid_search.
+    #
+    # See also: #idle
     def noop
       send_command("NOOP")
     end