Support biblatex subtitles in preview

[jspitz]

Is your suggestion for improvement related to a problem? Please describe.
I know that current CSL does not support subtitles (the next version, 1.1 or maybe bumped to 2.0, will [1,2]). Hence subtitles in biblatex mode are not displayed in preview, which of course hides central parts of the entry.

Describe the solution you'd like
I was wondering whether it would be feasible, for CSL up to 1.0.x, to merge subtitles into titles for preview.

Additional context
One drawback is that title-subtitle separators (e.g. colon vs. dot) are dependent on style. So this would either need to be hardcoded or maybe an option to customize it could be provided.
If jabref is able to detect on the currently used CSL version, this workaround support could stay for longer. It seems that the next version will be a major style change, so old styles might persist for a while.

[1] https://citationstyles.org/2020/07/11/seeking-public-comment-on-CSL-1-0-2/
[2] https://discourse.citationstyles.org/t/handling-main-sub-title-splits-citeproc-js/1563/16

[Siedlerchr]

Hm, we use this library and I don't know if it supports subtitles https://github.com/michel-kraemer/citeproc-java
It's currently CSL 1.0.1 compliant

[jspitz]

Hm, we use this library and I don't know if it supports subtitles https://github.com/michel-kraemer/citeproc-java It's currently CSL 1.0.1 compliant

I might be talking nonsense, as I am neither familiar with the code nor versed in Java programming, but wouldn't it just be a matter of merging the respective *subtitle fields into their *title correspondences before the data is being passed to that library? AFAICS this would be in bibEntryToCSLItemData of the jabrefItemDataProvider module, where currently already some mapping (number -> issue) is done in the biblatex case before the data is passed on.

[koppor]

If someone investigates, that one needs to check the library if it supports the subtitle. If no, open an issue. Then try to understand that library to support that feature. After that library supports it, add support to JabRef.