Rewrite some of the thorny pieces

draft-ietf-quic-qpack.md

@@ -251,18 +251,18 @@ header block might reference an entry in the dynamic table that has not yet been
 received.
 
 Each header block contains the total number of entries added to the dynamic
-table - the Insert Count - which identifies the table state necessary for
-decoding (see {{header-prefix}}). If the Insert Count is greater than the number
-of dynamic table entries received, the stream is considered "blocked."  While
-blocked, header field data SHOULD remain in the blocked stream's flow control
-window.  When the Insert Count is zero, the frame contains no references to the
-dynamic table and can always be processed immediately. A stream becomes
-unblocked when the number of entries inserted in the dynamic table becomes
-greater than or equal to the Insert Count for all header blocks the decoder has
-started reading from the stream.  If the decoder encounters a header block where
-the largest Absolute Index used not equal to the largest value permitted by the
-Insert Count, it MAY treat this as a stream error of type
-HTTP_QPACK_DECOMPRESSION_FAILED.
+table - the Required Insert Count - which identifies the table state necessary
+for decoding (see {{header-prefix}}). If the Required Insert Count is greater
+than the number of dynamic table entries received, the stream is considered
+"blocked."  While blocked, header field data SHOULD remain in the blocked
+stream's flow control window.  When the Required Insert Count is zero, the frame
+contains no references to the dynamic table and can always be processed
+immediately. A stream becomes unblocked when the number of entries inserted in
+the dynamic table becomes greater than or equal to the Required Insert Count for
+all header blocks the decoder has started reading from the stream.  If the
+decoder encounters a header block where the largest Absolute Index used not
+equal to the largest value permitted by the Required Insert Count, it MAY treat
+this as a stream error of type HTTP_QPACK_DECOMPRESSION_FAILED.
 
 The SETTINGS_QPACK_BLOCKED_STREAMS setting (see {{configuration}}) specifies an
 upper bound on the number of streams which can be blocked. An encoder MUST limit
@@ -283,12 +283,13 @@ encoder becoming blocked on congestion or flow control limits.
 
 ### Known Received Count
 
-In order to identify which dynamic table entries can be safely used
-without a stream becoming blocked, the encoder tracks the absolute index of the
-decoder's Known Received Count entry.
+In order to identify which dynamic table entries can be safely used without a
+stream becoming blocked, the encoder tracks the number of entries received by
+the decoder.  TheKnown Received Count tracks the total number of acknowledged
+insertions.
 
 When blocking references are permitted, the encoder uses header block
-acknowledgement to identify the Known Received Count index, as described in
+acknowledgement to identify the Known Received Count, as described in
 {{header-acknowledgement}}.
 
 To acknowledge dynamic table entries which are not referenced by header blocks,
@@ -335,9 +336,9 @@ acknowledged before using it.
 
 ### Blocked Decoding
 
-To track blocked streams, the necessary Insert Count value for each stream
-can be used.  Whenever the decoder processes a table update, it can begin
-decoding any blocked streams that now have their dependencies satisfied.
+To track blocked streams, the Required Insert Count value for each stream can be
+used.  Whenever the decoder processes a table update, it can begin decoding any
+blocked streams that now have their dependencies satisfied.
 
 
 # Header Tables
@@ -475,15 +476,18 @@ d = count of entries dropped
 Because frames from request streams can be delivered out of order with
 instructions on the encoder stream, relative indices are relative to the Base at
 the beginning of the header block (see {{header-prefix}}). The Base is encoded
-as a value relative to the Insert Count, so it can be expressed as the number of
-entries inserted. The dynamic table entries up to the Base can be referenced.
-The most recently inserted entry within the limit set by the Base has a relative
-index of 0.
+as a value relative to the Required Insert Count. The Base identifies which
+dynamic table entries can be referenced using relative indexing, starting with 0
+at the last entry added.
+
+Post-base references are used for entries inserted after base, starting at 0 for
+the first entry added after Base, see {{post-base}}.
 
 Though new entries could be added while processing a header block, the relative
 indices of entries do not change.
 
 ~~~~~ drawing
+ Required
   Insert
   Count      Base
     |         |
@@ -499,7 +503,8 @@ d = count of entries dropped
 ~~~~~
 {: title="Example Dynamic Table Indexing - Relative Index on Request Stream"}
 
-### Post-Base Indexing
+
+### Post-Base Indexing {#post-base}
 
 A header block on the request stream can reference entries added after the entry
 identified by the Base. This allows an encoder to process a header block in a
@@ -529,8 +534,9 @@ d = count of entries dropped
 
 If the decoder encounters a reference on a request or push stream to a dynamic
 table entry which has already been evicted or which has an absolute index
-greater than allowed by the declared Insert Count (see {{header-prefix}}), it
-MUST treat this as a stream error of type `HTTP_QPACK_DECOMPRESSION_FAILED`.
+greater than allowed by the declared Required Insert Count (see
+{{header-prefix}}), it MUST treat this as a stream error of type
+`HTTP_QPACK_DECOMPRESSION_FAILED`.
 
 If the decoder encounters a reference on the encoder stream to a dynamic table
 entry which has already been dropped, it MUST treat this as a connection error
@@ -733,12 +739,12 @@ connection error of type `HTTP_QPACK_DECODER_STREAM_ERROR`.
 
 ### Header Acknowledgement
 
-After processing a header block whose declared Insert Count is not zero, the
-decoder emits a Header Acknowledgement instruction on the decoder stream.  The
-instruction begins with the '1' one-bit pattern and includes the request
-stream's stream ID, encoded as a 7-bit prefix integer.  It is used by the peer's
-encoder to know when it is safe to evict an entry, and possibly update the Known
-Received Count.
+After processing a header block whose declared Required Insert Count is not
+zero, the decoder emits a Header Acknowledgement instruction on the decoder
+stream.  The instruction begins with the '1' one-bit pattern and includes the
+request stream's stream ID, encoded as a 7-bit prefix integer.  It is used by
+the peer's encoder to know when it is safe to evict an entry, and possibly
+update the Known Received Count.
 
 ~~~~~~~~~~ drawing
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@@ -755,17 +761,17 @@ processed in order, this gives the encoder precise feedback on which header
 blocks within a stream have been fully processed.
 
 If an encoder receives a Header Acknowledgement instruction referring to a
-stream on which every header block with a non-zero Insert Count has already been
-acknowledged, that MUST be treated as a connection error of type
+stream on which every header block with a non-zero Required Insert Count has
+already been acknowledged, that MUST be treated as a connection error of type
 `HTTP_QPACK_DECODER_STREAM_ERROR`.
 
 When blocking references are permitted, the encoder uses acknowledgement of
 header blocks to update the Known Received Count.  If a header block was
 potentially blocking, the acknowledgement implies that the decoder has received
-all dynamic table state necessary to process the header block.  If the Insert
-Count of an acknowledged header block was greater than the encoder's current
-Known Received Count, the block's Insert Count becomes the new Known Received
-Count.
+all dynamic table state necessary to process the header block.  If the Required
+Insert Count of an acknowledged header block was greater than the encoder's
+current Known Received Count, the block's Required Insert Count becomes the new
+Known Received Count.
 
 
 ### Stream Cancellation
@@ -804,12 +810,12 @@ streams emit the headers for an HTTP request or response.
 
 ### Header Data Prefix {#header-prefix}
 
-Header data is prefixed with two integers, `Insert Count` and `Base`.
+Header data is prefixed with two integers, `Required Insert Count` and `Base`.
 
 ~~~~~~~~~~  drawing
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 +---+---+---+---+---+---+---+---+
-|       Insert Count (8+)       |
+|   Required Insert Count (8+)  |
 +---+---------------------------+
 | S |      Delta Base (7+)      |
 +---+---------------------------+
@@ -922,8 +928,8 @@ field is represented as an integer with a 6-bit prefix (see Section 5.1 of
 
 If the entry is in the dynamic table with an absolute index greater than Base,
 the representation starts with the '0001' 4-bit pattern, followed by the
-post-base index (see {{post-base-indexing}}) of the matching header field,
-represented as an integer with a 4-bit prefix (see Section 5.1 of [RFC7541]).
+post-base index (see {{post-base}}) of the matching header field, represented as
+an integer with a 4-bit prefix (see Section 5.1 of [RFC7541]).
 
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@@ -976,7 +982,7 @@ static (S=1) or dynamic (S=0) table.
 
 For entries in the dynamic table with an absolute index greater than the Base,
 the header field name is represented using the post-base index of that entry
-(see {{post-base-indexing}}) encoded as an integer with a 3-bit prefix.
+(see {{post-base}}) encoded as an integer with a 3-bit prefix.
 
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