There are several more-complex-than-typical citation/bibliography formats that CSL doesn’t currently support. I am wondering what folks’ dispositions are toward expanding support for these, such as in CSL 1.2 or 2.0. If there is general interest in supporting these formats, I can draft some specification text for them.
Compound numeric citations. (See https://github.com/citation-style-language/schema/issues/36).
In chemistry, it’s common to cite multiple related items within one citation number (e.g., 1a. XXX, 1b. YYY, 1c. ZZZ). Generally, subsequent citations would cite the set of these citations as a whole, but referring to a specific item in a subsequent citation by itself (e.g., citing just “1b”) is possible.
Support for this format would require a new option for enumerating
Nested/cross-referenced items. (e.g., https://forums.zotero.org/discussion/80336/nested-citation-for-book-chapters)
Some citation styles, such as Annual Reviews or the Unified Stylesheet for Linguistics, want a format where chapters and the book containing them are listed separately in the bibliography. For example:
Connors 2019: The ideal title. In: Abel & al. 2019, pp. 35-78.
Abel & al. 2019: The complete title of the book, Abel A., Connors C. & Zimmer Z. (eds.), London 2019.
Generally, such styles (all that I am aware), would require this formatting if there is more than one chapter from the same book, but would do a more typical chapter citation (all in one bibliography entry) if only one chapter from a book is cited.
Such formats could be supported by implementing a formal hierarchical item system, but a less invasive change to CSL would be a simpler matching system, such as matching items on
editortranslator and merging items that match on these variables.
Bibliographies with subsections. (e.g., https://forums.zotero.org/discussion/79532/blibliographie-classee-par-type-de-references and elsewhere)
Many different fields require bibliographies with subsections, such as primary vs secondary sources; in-text citations vs data/artifact citations (e.g., references for the data, films, or artwork analyzed); general citations versus items considered in a systematic review; separate sections for items in different languages. The current recommended process for such styles is to use a macro to sort citations into the needed categories, then include this macro as the first sort key in the bibliography. The limitation of this approach is that subheadings describing the sections aren’t possible.
When using CSL with traditional clients integrating with word processors, this isn’t a huge limitation, as the subheadings can be added as a final step after writing, but CSL is increasingly being used to generate fully reproducible documents using pandoc-citeproc or other processors, which makes this approach much more limiting.
Supporting these forms would require adding to option to specify something like
group_by within the bibliography, with the ability to specify heading text for each section. Jurism/CSLm has had a similar feature for some time supporting separating sections of a bibliography by language.