Reorder Extension Headers (#1379)

To minimize the diff with #1374

Author: ianswett

draft-ietf-moq-transport.md

@@ -3697,38 +3697,6 @@ SUBGROUP_HEADER {
 
 The following Object Extension Headers are defined in MOQT.
 
-## Prior Group ID Gap
-
-Prior Group ID Gap (Extension Header Type 0x3C) is a variable length integer
-containing the number of Groups prior to the current Group that do not and will
-never exist. For example, if the Original Publisher is publishing an Object in
-Group 7 and knows it will never publish any Objects in Group 8 or Group 9, it
-can include Prior Group ID Gap = 2 in any number of Objects in Group 10, as it
-sees fit.  A Track is considered malformed (see {{malformed-tracks}}) if any of
-the following conditions are detected:
-
- * An Object contains more than one instance of Prior Group ID Gap.
- * A Group contains more than one Object with different values for Prior Group
-    ID Gap.
- * An Object has a Prior Group ID Gap larger than the Group ID.
- * An endpoint receives an Object with a Prior Group ID Gap covering an Object
-   it previously received.
- * An endpoint receives an Object with a Group ID within a previously
-   communicated gap.
-
-This extension is optional, as publishers might not know the prior gap gize, or
-there may not be a gap. If Prior Group ID Gap is not present, the receiver
-cannot infer any information about the existence of prior groups (see
-{{group-ids}}).
-
-This extension can be added by the Original Publisher, but MUST NOT be added by
-relays. This extension MAY be removed by relay when the object in question is
-served via FETCH, and the gap that the extension communicates is already
-communicated implicitly in the FETCH response; it MUST NOT be modified or
-removed otherwise.
-
-An Object MUST NOT contain more than one instance of this extension header.
-
 ## Immutable Extensions
 
 The Immutable Extensions (Extension Header Type 0xB) contains a sequence of
@@ -3775,6 +3743,38 @@ EXT 1 and EXT N can be modified or removed by Relays
 
 An Object MUST NOT contain more than one instance of this extension header.
 
+## Prior Group ID Gap
+
+Prior Group ID Gap (Extension Header Type 0x3C) is a variable length integer
+containing the number of Groups prior to the current Group that do not and will
+never exist. For example, if the Original Publisher is publishing an Object in
+Group 7 and knows it will never publish any Objects in Group 8 or Group 9, it
+can include Prior Group ID Gap = 2 in any number of Objects in Group 10, as it
+sees fit.  A Track is considered malformed (see {{malformed-tracks}}) if any of
+the following conditions are detected:
+
+ * An Object contains more than one instance of Prior Group ID Gap.
+ * A Group contains more than one Object with different values for Prior Group
+    ID Gap.
+ * An Object has a Prior Group ID Gap larger than the Group ID.
+ * An endpoint receives an Object with a Prior Group ID Gap covering an Object
+   it previously received.
+ * An endpoint receives an Object with a Group ID within a previously
+   communicated gap.
+
+This extension is optional, as publishers might not know the prior gap gize, or
+there may not be a gap. If Prior Group ID Gap is not present, the receiver
+cannot infer any information about the existence of prior groups (see
+{{group-ids}}).
+
+This extension can be added by the Original Publisher, but MUST NOT be added by
+relays. This extension MAY be removed by relay when the object in question is
+served via FETCH, and the gap that the extension communicates is already
+communicated implicitly in the FETCH response; it MUST NOT be modified or
+removed otherwise.
+
+An Object MUST NOT contain more than one instance of this extension header.
+
 ## Prior Object ID Gap
 
 Prior Object ID Gap (Extension Header Type 0x3E) is a variable length integer