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Requests within a "flexible version" will have a new version of the request header.  The new RequestHeader version will be version 1, superseding version 0.  In this new version, the RequestHeader's ClientId string will be a COMPACT_STRING rather than  STRING.  Additionally, the header will contain space for tagged fields at the end.  Supporting tagged fields in the request header will give us a natural place to put additional information that is common to all requests.

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Responses within a "flexible version" will have a new version of the response header.  The new ResponseHeader version will be version 1, superseding version 0.  In this new version, the header will contain space for tagged fields at the end.  Supporting Supporting tagged fields in the response header will give us a natural place to put additional information that is common to all responses.

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In a flexible version, each structure begins ends with a tag section.  This section stores all of the tagged fields in the structure.

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All requests and responses will begin end with a tagged field buffer.  If there are no tagged fields, this will only be a single zero byte.

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