[Cbor] ref'' and standins (draft-bormann-cbor-e-ref, draft-bormann-cbor-yang-standin)

[Christian Amsüss <[e-mail]>]

Hello Carsten, group,

looking at both e-ref and standins in close succession, I think there is
a commonality that can be exploited.

Currently, ref'' is limited to use within EDN (except when expressed as
`CPA999(["ref", "filename.diag")`), and pulls a value from a file.
Stand-in tags are CBOR tags that suply infromation in an equivalent but
more efficient format (which is also what ref does, even though none of
the tags defined in standin currently considers context in its
conversion).

The common pattern is that there is a CBOR item (or pseudoitem, in the
ref'' case) that really means what is referenced in its description.

Other occurrences where we have similar mechanisms are bare hash
values from notable-tags (which are not explicit about standing in for
the hash's content, but AIU worked that way in their original use case),
and packed-by-reference, which produces something similar using
`TBD1114(1, "http://example.com/path", simple(0))` (although the
identifier does not describe a CBOR item here, but 1-long item list
whose only item is the desired item).

Could this be generalized in the yang-standin document, or (if it
exceeds its scope) in a generalized stand-in concept? Then, ref'' could
be redefined to merely be a short-hand for some tag around the given URI
reference, and serve as a hint to the reader that this kind of stand-in
is better resolved before processing the document.

Best regards
Christian

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