"Attachments" used throughout the text but unclear at first reading.

[daidoji]

In https://trustoverip.github.io/tswg-cesr-specification/#terms-and-definitions we have the definition

Message
Consists of a serialized data structure that comprises its body and a set of serialized data structures that are its attachments. Attachments may include but are not limited to signatures on the body.

This could be considered sufficient as we do specify that they're just serialized data structures that follow the message but is a bit confusing as a reader until you find this definition (with sub-definition for attachments embedded).

I wasn't quite sure though how to fix this in a PR so I created this issue so that wiser heads than mine could think about it. It came up as I'm working with my partner who doesn't really read the specs as closely as I do and there was some ambiguity until we searched around for a bit in the spec.

A fix for this issue might be one or more of the following (but I don't know which is best):

1. More concrete representations in the spec with "message" and "attachments" that will come over the wire clearly specified.
2. Another definition for "attachment" specifically pulled out from that message definition above.
3. A general description in "Composability and Domain Representations" section of Messages and Attachments of what these things will look like over the wire (maybe just in the text domain with a link to how it can be sent in the binary domain).

[pfeairheller]

Discussed 2024-02-13: We should promote the mention of "Attachment" in the definition of "Message" to its own definition.

[SmithSamuelM]

Added description of messages as message body plus attachments to introduction. Added explanitory text for self-framing groups not just primiitives.

[SmithSamuelM]

Woops. still need definition of Attachment separate from Message, Message Body