Allow multiple citation templates

[bdarcus]

Per discussion starting at https://github.com/citation-style-language/schema/pull/173#issuecomment-1142418272 (but also preceding it above), this is an alternative to #193.

The idea is to revert that, and replace it with a more general solution: multiple citation templates.

Example:

<citation mode="default">
...
</citation>
<citation mode="in-text">
...
</citation>
<citation mode="bib-entry">
...
</citation>

Notes

1. The primary use case that both this and #193 are supporting is major styles like APA which require different author list formatting in text and in parens. In that case, one must specify those details in the style for it to work as expected.
2. That last example isn't supported in the initial commit, but also shows a wrinkle; really there we want to say to use the bibliography template for rendering the citation.
3. Also larger context: we could imagine also multiple bibliography elements, for multi-section bibs and such, but that's out-of-scope here.
4. I haven't figured out how to revert #193 in git, but if not, it's easy enough to just remove the lines here.
5. Another approach would be multiple layouts within a single citation. I've not thought about the details enough to know ATM which is better.

Related questions

Many existing citeprocs (for js, elisp, haskell, and rust) already support implicit "suppress-author" and "in-text" commands.

Thoughts on how to handle this?

I see a few options, which aren't necessarily mutually-exclusive:

1. document the logic for these (both suppress-author and in-text)
2. use 1 to automate style updates
3. require 1.1/2.0-compliant processors to support 1 also (which means works with 1.0 also)
4. leave 1 optional

CC @bwiernik @denismaier @andras-simonyi @jgm @zepinglee @cormacrelf

If there are objections, I can also just close this PR. But I wanted to discuss something concrete.

[denismaier]

I like this suggestion as it will make the syntax more extensible and uniform.

Another approach would be multiple layouts within a single citation. I've not thought about the details enough to know ATM which is better.

Yes, I think, somewhere along the way, I've proposed multiple layouts too, each for a mode. But I'm also unsure if either of those has particular drawbacks compared to the other.

Also larger context: we could imagine also multiple bibliography elements, for multi-section bibs and such, but that's out-of-scope here.

Good suggestion. That could come in handy for international and legal matters... (even if that is out of scope). Also, that could help with things such as abbreviation lists.

Obviously, there are couple of details we'd need to work out...

[bdarcus]

After experimenting with Denis, I'm closing this.

I think the right solution is to allow cs:choose as a child of cs:citation, and adding a new cs:mode conditional attribute.

[bwiernik]

Agreed