[connect-tcp] Reword "100 (Continue)" requirement

Fixes #2717

draft-ietf-httpbis-connect-tcp.md

@@ -159,7 +159,7 @@ Servers that host a proxy under this specification MAY offer support for TLS ear
 
 ## Conveying metadata
 
-This specification supports the "Expect: 100-continue" request header ({{?RFC9110, Section 10.1.1}}) in any HTTP version.  The "100 (Continue)" status code confirms receipt of a request at the proxy without waiting for the proxy-destination TCP handshake to succeed or fail.  This might be particularly helpful when the destination host is not responding, as TCP handshakes can hang for several minutes before failing.  Implementation of "100 (Continue)" support is OPTIONAL for clients and REQUIRED for proxies.
+This specification supports the "Expect: 100-continue" request header ({{?RFC9110, Section 10.1.1}}) in any HTTP version.  The "100 (Continue)" status code confirms receipt of a request at the proxy without waiting for the proxy-destination TCP handshake to succeed or fail.  This might be particularly helpful when the destination host is not responding, as TCP handshakes can hang for several minutes before failing.  Clients MAY send "Expect: 100-continue", and proxies MUST respect it by returning "100 (Continue)" if the request is not immediately rejected.
 
 Proxies implementing this specification SHOULD include a "Proxy-Status" response header {{!RFC9209}} in any success or failure response (i.e., status codes 101, 2XX, 4XX, or 5XX) to support advanced client behaviors and diagnostics.  In HTTP/2 or HTTP/3, proxies MAY additionally send a "Proxy-Status" trailer in the event of an unclean shutdown.