Adding note about suites with unknown properties and their effect

draft-ietf-httpbis-http2.xml

@@ -3673,6 +3673,11 @@ HTTP2-Settings    = token68
             Authenticated Encryption with Additional Data (AEAD) modes, such as the <xref
             target="RFC5288">Galois Counter Model (GCM) mode for AES</xref> are acceptable.
           </t>
+          <t>
+            HTTP/2 implementations MUST NOT offer or select cipher suites that have unknown
+            properties with respect to these properties.  This avoids situations where peers
+            disagree about whether a given cipher suite is permitted.
+          </t>
           <t>
             The effect of these restrictions is that TLS 1.2 implementations could have
             non-intersecting sets of available cipher suites, since these prevent the use of the