Clarify server behavior when negotiating version with preferred_versions
@@ -1973,10 +1973,13 @@ typedef struct ngtcp2_settings {
* of preference.
*
* On compatible version negotiation, server will negotiate one of
- * those versions contained in this array if a client initially
- * chooses a less preferred version. This version set corresponds
- * to Offered Versions in QUIC Version Negotiation draft, and it should
- * be sent in Version Negotiation packet.
+ * those versions contained in this array if there is some overlap
+ * between these versions and the versions offered by the client.
+ * If there is no overlap, but the client chosen version is
+ * supported by the library, the server chooses the client chosen
+ * version as the negotiated version. This version set corresponds
+ * to Offered Versions in QUIC Version Negotiation draft, and it
+ * should be included in Version Negotiation packet.
*
* Client uses this field and :member:`original_version` to prevent
* version downgrade attack if it reacted upon Version Negotiation
