Stop using 'fields' for ACK Range and Gap, tweak structure a little

draft-ietf-quic-transport.md

@@ -2853,12 +2853,12 @@ if the sender includes them in packets with non-ACK frames.  A sender SHOULD
 bundle ACK frames with other frames when possible.
 
 To limit receiver state or the size of ACK frames, a receiver MAY limit the
-number of ACK Range fields it sends.  A receiver can do this even without
-receiving acknowledgment of its ACK frames, with the knowledge this could cause
-the sender to unnecessarily retransmit some data.  Standard QUIC
-{{QUIC-RECOVERY}} algorithms declare packets lost after sufficiently newer
-packets are acknowledged.  Therefore, the receiver SHOULD repeatedly acknowledge
-newly received packets in preference to packets received in the past.
+number of ACK Ranges it sends.  A receiver can do this even without receiving
+acknowledgment of its ACK frames, with the knowledge this could cause the sender
+to unnecessarily retransmit some data.  Standard QUIC {{QUIC-RECOVERY}}
+algorithms declare packets lost after sufficiently newer packets are
+acknowledged.  Therefore, the receiver SHOULD repeatedly acknowledge newly
+received packets in preference to packets received in the past.
 
 
 ### ACK Frames and Packet Protection
@@ -4200,27 +4200,30 @@ ACK Range Count:
 First ACK Range:
 
 : A variable-length integer indicating the number of contiguous packets
-  preceding the Largest Acknowledged that are being acknowledged.
+  preceding the Largest Acknowledged that are being acknowledged.  The First ACK
+  Range is encoded as an ACK Range (see {{ack-ranges}}) starting from the
+  Largest Acknowledged.  That is, the smallest packet number included in the
+  range is determined by subtracting the First ACK Range value from the Largest
+  Acknowledged.
 
 ACK Ranges:
 
 : Contains additional ranges of packet numbers which are alternately not
-  acknowledged (Gap) and acknowledged (ACK Range), see {{ack-ranges-section}}.
+  acknowledged (Gap) and acknowledged (ACK Range), see {{ack-ranges}}.
 
 ECN Counters:
 
 : The three ECN Counters, see {{ack-ecn-counters}}.
 
 
-### ACK Ranges Section {#ack-ranges-section}
+### ACK Ranges {#ack-ranges}
 
-The ACK Range Section consists of alternating Gap and ACK Range fields in
-descending packet number order.  The First Ack Range field is followed by a
-variable number of alternating Gap and ACK Range fields.  The number of Gap and
-ACK Range fields is determined by the ACK Range Count field; one of each field
-is present for each value in the ACK Range Count field.
+The ACK Ranges field consists of alternating Gap and ACK Range values in
+descending packet number order.  The number of Gap and ACK Range values is
+determined by the ACK Range Count field; one of each value is present for each
+value in the ACK Range Count field.
 
-The ACK Ranges field is structured as follows:
+ACK Ranges are structured as follows:
 
 ~~~
  0                   1                   2                   3
@@ -4243,14 +4246,28 @@ The ACK Ranges field is structured as follows:
 ~~~
 {: #ack-range-format title="ACK Ranges"}
 
-Gap and ACK Range fields use a relative integer encoding for efficiency.  Though
+The fields that form the ACK Ranges are:
+
+Gap (repeated):
+
+: A variable-length integer indicating the number of contiguous unacknowledged
+  packets preceding the packet number one lower than the smallest in the
+  preceding ACK Range.
+
+ACK Range (repeated):
+
+: A variable-length integer indicating the number of contiguous acknowledged
+  packets preceding the largest packet number, as determined by the
+  preceding Gap.
+
+Gap and ACK Range value use a relative integer encoding for efficiency.  Though
 each encoded value is positive, the values are subtracted, so that each ACK
 Range describes progressively lower-numbered packets.
 
 Each ACK Range acknowledges a contiguous range of packets by indicating the
 number of acknowledged packets that precede the largest packet number in that
 range.  A value of zero indicates that only the largest packet number is
-acknowledged.  Larger ACK range values indicate a larger range, with
+acknowledged.  Larger ACK Range values indicate a larger range, with
 corresponding lower values for the smallest packet number in the range.  Thus,
 given a largest packet number for the range, the smallest value is determined by
 the formula:
@@ -4259,42 +4276,26 @@ the formula:
    smallest = largest - ack_range
 ~~~
 
-The packets that are acknowledged by the ACK Range include the range from the
-smallest packet number to the largest, inclusive.
+An ACK Range acknowledges all packet numbers between the smallest packet number
+and the largest, inclusive.
 
-The largest packet number value for the First ACK Range is determined by the
-Largest Acknowledged field; the largest value for subsequent ACK Range fields is
-determined by cumulatively subtracting the size of all preceding ACK Range and
-Gap fields.
+The largest value for an ACK Range is determined by cumulatively subtracting the
+size of all preceding ACK Ranges and Gaps.
 
-Each Gap field indicates a range of packets that are not being acknowledged.
-The number of packets in the gap is one higher than the encoded value of the Gap
+Each Gap indicates a range of packets that are not being acknowledged.  The
+number of packets in the gap is one higher than the encoded value of the Gap
 field.
 
 The value of the Gap field establishes the largest packet number value for the
-ACK Range that follows the gap using the following formula:
+subsequent ACK Range using the following formula:
 
 ~~~
   largest = previous_smallest - gap - 2
 ~~~
 
-If the calculated value for largest or smallest packet number for any ACK Range
-is negative, an endpoint MUST generate a connection error of type
-FRAME_ENCODING_ERROR indicating an error in an ACK frame.
-
-The fields that form the ACK Ranges field are:
-
-Gap (repeated):
-
-: A variable-length integer indicating the number of contiguous unacknowledged
-  packets preceding the packet number one lower than the smallest in the
-  preceding ACK Range.
-
-ACK Range (repeated):
-
-: A variable-length integer indicating the number of contiguous acknowledged
-  packets preceding the largest packet number, as determined by the
-  preceding Gap.
+If any computed packet number is negative, an endpoint MUST generate a
+connection error of type FRAME_ENCODING_ERROR indicating an error in an ACK
+frame.
 
 
 ### ECN Counters {#ack-ecn-counters}
@@ -4318,7 +4319,7 @@ The ECN section consists of three counters (see {{ecn-counters}}) as follows:
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~~~
 
-The fields that form the ECN Counters field are:
+The fields that form the ECN Counters are:
 
 ECT(0) Count:
 : A variable-length integer representing the total number packets received with