Applying Martin Thomson's suggested fixes for restructuring.

draft-ietf-quic-transport.md

@@ -3013,9 +3013,9 @@ an ACK frame without ECN feedback, the endpoint stops setting ECT codepoints in
 subsequent IP packets, with the expectation that either the network path or the
 peer no longer supports ECN.
 
-To protect the connection from arbitrary corruption of ECN codepoints by
-elements on the network path, an endpoint verifies the following when an ACK
-frame is received:
+To reduce the risk of non-standard compliant ECN markings affecting the
+operation of an endpoint, an endpoint verifies the counts it receives when it
+receives new acknowledgements:
 
 * The increase in ECT(0) and ECT(1) counters MUST be at least the number of QUIC
   packets newly acknowledged that were sent with the corresponding codepoint
@@ -3027,14 +3027,13 @@ frame is received:
   this ACK frame. This detects if the network changes ECT(0), ECT(1) or CE to
   Not-ECT.
 
-If the sender does not have state to determine if a particular packet number is
-newly acknowledged or not, then the verifications using this acknowledgement
-cannot be performed. If an acknowledgement arrive with a packet number that
-isn't the highest to arrived so far, i.e. some reordering has occured, then the
-verification may fail erronously. To prevent this the sender MUST NOT perform
-ECN verification using older acknwoeldgements. By the end of the verification
-process the local reference counter must have be updated to include the newly
-acknowledged packets.
+This validation is only performed if the ACK frame increases the largest
+received packet number. Reordered acknowledgments could have lower counter
+values and might not be successfully validated as a result.
+
+These counts might be inflated if acknowledgments are never received for packets
+that were successfully delivered. If validation succeeds, an endpoint MUST
+increase its expected counter values to those it receives.
 
 An endpoint could miss acknowledgements for a packet when ACK frames are lost.
 It is therefore possible for the total increase in ECT(0), ECT(1), and CE