Loosen prohibition on unknown stream types further

Author: MikeBishop

draft-ietf-quic-http.md

@@ -503,10 +503,10 @@ unknown. Recipients of unknown stream types MAY trigger a QUIC STOP_SENDING
 frame with an error code of HTTP_UNKNOWN_STREAM_TYPE, but MUST NOT consider such
 streams to be an error of any kind.
 
-Implementations SHOULD NOT send stream types the peer is not already known to
-support.   Stream types which could modify the state or semantics of existing
-protocol components, including QPACK or other extensions, MUST NOT be sent until
-the peer is known to support them.
+Implementations MAY send stream types before knowing whether the peer supports
+them.  However, stream types which could modify the state or semantics of
+existing protocol components, including QPACK or other extensions, MUST NOT be
+sent until the peer is known to support them.
 
 ### Reserved Stream Types {#stream-grease}