arXiv: Stop populating Extra

[dstillman]

zotero/zotero#5680 (comment)

Since we're populating Repository/Archive ID. Not sure if we want to put the category ("astro-ph") somewhere.

[alex-ter]

I'll take this one and #3565. As for the archive (that's what they seem to call this value), I think it's helpful to have it. Maybe a dedicated note? I guess none of the existing fields (such as Genre or Archive) would fit.

[alex-ter]

There's also been a discussion upon introducing the preprint type: this comment and on, with an argument that arXiv itself lists the "archive" value in the "Cite as" suggestion (it still does AFAICS).

[alex-ter]

Any further thoughts for this one? Thinking more about it, and taking the arXiv's own recommendations on how to reference the papers, I'd say having the category or "archive", or whatever the right name is (they seem to be inconsistent with the naming across different documentation pieces) does make sense, as it's part of the recommended reference format.

Coincidentally, there's a recent PR #3577, making the subcategory or "subject class" (as per the below quote) appear in what's currently saved in the Extra field, so apparently people do use that beyond that formal recommendation.

Here's an excerpt (emphasis mine):

You should use references of the form:

arXiv:YYMM.NNNNv# [category] for new paper identifiers (April 2007 onward), e.g. arXiv:0706.1234v1 [math.FA].

arXiv:arch-ive/YYMMNNNv# or arXiv:arch-ive/YYMMNNNv# [category] for papers submitted before April 2007. The second form should be used for archives that have subject classes (math.XX, cs.XX etc.), e.g.
arXiv:hep-th/9901001v3
or
arXiv:math/9910001v1 [math.AT].
[...]
These forms are shown on the abstract web pages labeled Cite as:, and the identifier part is linked to the correct URL for the abstract page.
[...]
If you wish to be less specific, you may omit the explicit version number by omitting the v# part of the identifier in which case the latest version will be shown, for example:

arXiv:0706.1234 [math.FA]
arXiv:hep-th/9910001

There should not be any spaces or punctuation other than as shown above. We encourage the inclusion of the primary subject area in square brackets after references to papers with new identifiers; this isn't necessary to identify the paper but may help readers understand a citation more easily.

Which field do you think would suit here? Maybe Genre, after all?