Attachment metadata

[fluffy-critter]

Expected Behavior

There should be some means of providing metadata associated with an attachment relationship, beyond just the fact the attachment exists.

Additionally, attachment order should probably be made stable and explicit.

Current Behavior

There is no way to associate metadata with an attachment without it being put on the attached item itself, which is not sufficient for some use cases.

Context

In building a site that uses Publ to manage information about music, a situation arises when the same track appears on multiple albums. For example, if Album1.md and Album2.md both attach HitSingle.md, but it has a different playlist position on both albums, there is no straightforward way to reflect that in the current attachment mechanism.

Currently on https://sockpuppet.band/ every track has a Track-Number position which is used to sort it on the containing album, but that assumes there is only one containing album. A "best-of" collection (or an alternate edition with the same track recordings) would lead to an inconsistency.