Clarify End of track (#635)

Fixes #505.

draft-ietf-moq-transport.md

@@ -2147,11 +2147,18 @@ are beyond the end of a group or track.
          in this Group. This SHOULD be cached. A publisher MAY use an end of
          Group object to signal the end of all open Subgroups in a Group.
 
-* 0x4 := Indicates end of Track and Group. GroupID is one greater than
-         the largest group produced in this track and the ObjectId is
-         one greater than the largest object produced in that
-         group. This is sent right after the last object in the
-         track. This SHOULD be cached.
+* 0x4 := Indicates end of Track and Group. GroupID is the largest group produced
+         in this track and the ObjectId is one greater than the largest object
+         produced in that group. An object with this status that has a Group ID
+         less than any other Group ID, or an Object ID less than or equal to the
+         largest in the group, is a protocol error, and the receiver MUST
+         terminate the session. This SHOULD be cached.
+
+* 0x5 := Indicates end of Track. GroupID is one greater than the largest group
+         produced in this track and the ObjectId is zero. An object with this
+         status that has a Group ID less than or equal to any other Group ID, or
+         an Object ID other than zero, is a protocol error, and the receiver
+         MUST terminate the session. This SHOULD be cached.
 
 Any other value SHOULD be treated as a protocol error and terminate the
 session with a Protocol Violation ({{session-termination}}).