Import RFC7540 recommendation to 431 on oversize headers; fixes #2775

draft-ietf-quic-http.md

@@ -484,11 +484,12 @@ HPACK which allows the flexibility to avoid header-compression-induced
 head-of-line blocking.  See that document for additional details.
 
 An HTTP/3 implementation MAY impose a limit on the maximum size of the header it
-will accept on an individual HTTP message; encountering a larger message header
-SHOULD be treated as a stream error of type `HTTP_EXCESSIVE_LOAD`.  The size of
-a header list is calculated based on the uncompressed size of header fields,
-including the length of the name and value in bytes plus an overhead of 32 bytes
-for each header field.
+will accept on an individual HTTP message.  A server that receives a larger
+header block than it is willing to handle can send an HTTP 431 (Request Header
+Fields Too Large) status code {{?RFC6585}}.  A client can discard responses that
+it cannot process.  The size of a header list is calculated based on the
+uncompressed size of header fields, including the length of the name and value
+in bytes plus an overhead of 32 bytes for each header field.
 
 If an implementation wishes to advise its peer of this limit, it can be conveyed
 as a number of bytes in the `SETTINGS_MAX_HEADER_LIST_SIZE` parameter. An