What is the recommended method for having a supplemental materials file when writing a manuscript using quarto? A supplemental materials file can contain sections, figures and tables that may be cited from the main text and vice-versa.
I can see in the scholarly writing portion of the Quarto guide features a section on Appendixes. However these appendixes are contained within the same output file.
Alternativley, one could use the book format, but this forces one to have a index.qmd in the root directory of the project and requires chapter numbering for cross-references between chapters. Furthermore, this does not exactly correspond to the structure of many journal articles where the main text has simple numbering (e.g. "Figure 1", "Figure 2") while the supplemental materials have numberings such as "Supplemental Figure 2", or "Figure S1".
I am not aware of any other possibilities other than just manually numbering cross-references, or using custom functions to have cross-references between a main and a supplemental quarto documents.