1 - pack data
2 - progress messages
3 - fatal error message just before stream aborts
+
+ server-option
+~~~~~~~~~~~~~~~
+
+If advertised, indicates that any number of server specific options can be
+included in a request. This is done by sending each option as a
+"server-option=<option>" capability line in the capability-list section of
+a request.
+
+The provided options must not contain a NUL or LF character.