Merge pull request #72 from SmithSamuelM/revised-format

fix issue #65

spec/spec.md

@@ -1220,7 +1220,7 @@ The first four characters, `PPPP` indicate the protocol. Each genus of a given C
 
 The next three characters, `VVV`, provide in Base64 notation the major and minor version numbers of the Version of the protocol specification. The first `V` character provides the major version number, and the final two `VV` characters provide the minor version number. For example, `CAA` indicates major version 2 and minor version 00 or in dotted-decimal notation, i.e., `2.00`. Likewise, `CAQ` indicates major version 2 and minor version decimal 16 or in dotted-decimal notation `1.16`. The Version part supports up to 64 major versions with 4096 minor versions per major version. 
 
-The next four characters, `KKKK` indicate the serialization kind in uppercase. The four supported serialization kinds are `JSON`, `CBOR`, `MGPK`, and `CESR` for the JSON, CBOR, MessagePack, and CESR serialization standards, respectively [[spec: RFC4627]] [[spec: RFC4627]] [[spec: RFC8949]] [[ref: RFC8949]] [[3]] [[ref: CESR]]. The last one, CESR, is used to represent `CESR` when the field map is converted to an in-memory data object so that it might be converted more conveniently back to the appropriate serialization. The native CESR serialization of a field map does not need a serialization type. 
+The next four characters, `KKKK` indicate the serialization kind in uppercase. The four supported serialization kinds are `JSON`, `CBOR`, `MGPK`, and `CESR` for the JSON, CBOR, MessagePack, and CESR serialization standards, respectively [[spec: RFC4627]] [[spec: RFC4627]] [[spec: RFC8949]] [[ref: RFC8949]] [[3]] [[ref: CESR]]. The last one, CESR is special. A CESR native serialization of a field map may use either the    `-G##` or  `-0G#####` count codes to indicate both that it is a field map and its size. Moreover, because count codes have unique start bits (see the section on Performant resynchronization) there is no need to embed a regular expression parsable version string field in a CESR native field map. Instead, a native CESR message's field map includes a protocol version field that indicates the protocol and version but not the size and serialization type. These are provided already by the count code. As a result, once deserialized into an in-memory data object representation of that field map, there is no normative indication that the in-memory object was deserialized from a  CESR native field map (i.e. no version string field with serialization kind).   This serialization kind indication would otherwise have to be provided externally.  Instead, the in-memory object representation of the field map may inject a placeholder version string, `v` field, whose value is a version string but with the serialization kind set to `CESR`. This way, when re-serializing, there is a normative indicator to reserialize as a CESR native field map, not JSON, CBOR, or MGPK.  This reserialization does not include an embedded version string field. It only appears in the in-memory object representation, not the serialization.
 
 The next four characters, `BBBB`, provide in Base64 notation the total length of the serialization, inclusive of the Version String and any prefixed characters or bytes. This length is the total number of characters in the serialization of the field map. The maximum length of a given field map serialization is thereby constrained to be 64<sup>4</sup> = 2<sup>24</sup> = 16,777,216 characters in length. This is deemed generous enough for the vast majority of anticipated applications. For serializations that may exceed this size, a secure hash chain of Messages may be employed where the value of a field in one Message is the cryptographic digest, SAID of the following Message. The total size of the chain of Messages may, therefore, be some multiple of 2<sup>24</sup>.