Biblatex doesn't recognize the journal's issue number when filled by a non-numeric value

Question

Sometimes, academic journal are published in a double issues. It results, in the .bib file, a reference with a field 'number' which is not set to '2' or '3', for instance, but set to '2-3'.

Here is what biblatex+biber gives :

SURNAME Name, "A Nice Title", Annual Review of Something 10 (2-3 1996).

Here is what I want to get :

SURNAME Name, "A Nice Title", Annual Review of Something. 10.2-3 (1996).

I precise that everything works well when the field 'number' of my .bib file is set with a value specifically numeric.

What's happening ?

[EDIT]

We've discussed on this issue on the github of the Zotero plugin called Better bibtex (here). A first step in answer is that such a functionning is normal. Indeed, the biblatex manual says (section 2.2.2) :

issue field (literal)

The issue of a journal. This field is intended for journals whose individual issues are identified by a designation such as ‘Spring’ or ‘Summer’ rather than the month or a number. Since the placement of issue is similar to month and number, this field may also be useful with double issues and other special cases. See also month, number, and § 2.3.9.

[...]

number: field (integer)

The number of a journal or the volume/number of a book in a series. See also issue as well as §§2.3.7 and 2.3.9. With @patent entries, this is the number or record token of a patent or patent request. It is expected to be an integer, not necessarily in arabic numerals since biber will automatically from roman numerals or arabic letter to integers internally for sorting purposes.

So it appears that Biblatex requires a integer value in the field number. If necessary, it recommends to avoid this limitation in using the field issue.

The problem remains that double issues do not render properly in this way.

Here is an example :

\documentclass{article}
\usepackage{filecontents}
\usepackage{polyglossia} 
\setmainlanguage{french}

\begin{filecontents}{\jobname.bib}
@article{Bob1996,
  title = {A {{Very Nice Title}}},
  volume = {10},
  number = {2},
  journaltitle = {Annual Review of Nothing},
  date = {1996},
  author = {Bob, Bob}
}

@article{John1996,
  title = {A {{Nice Title}}},
  volume = {10},
  issue = {2-3},
  journaltitle = {Annual Review of Something},
  date = {1996},
  author = {John, John}
}
\end{filecontents}

\usepackage[ 
backend=biber,citestyle=verbose,bibstyle=verbose,]{biblatex} 
\addbibresource{\jobname.bib} 

\begin{document}
Here is something\autocite{Bob1996} very interesting\autocite{John1996}.
\printbibliography
\end{document}

What gives (with xelatex+biber) :

Bob, Bob. “A Very Nice Title”. In : Annual Review of Nothing 10.2 (1996).

John, John. “A Nice Title”. In : Annual Review of Something 10 (2-3 1996).

Answer 1

For biblatex there are two possible fields to indicate the subdivision of a volume for @article and @periodical entries: number and issue. The go-to field is number and for most users that is the appropriate field even if the publisher calls the subdivision of a volume "issue". The issue field is printed closer to the date in the standard styles and can be used in case the number field gives unfortunate output.

In biblatex versions before 3.12 number was an integer field. This caused some export tools such as Better Bib(La)TeX for Zotero to only export integer values to number and use issue as a fallback for non-integer values. Since 2-3 is not an integer it was exported to issue. The output for number = {2-3} is also acceptable and arguably nicer than with issue = {2-3}, so it was decided that number should not be restricted to integer input any more: https://github.com/plk/biblatex/issues/726

The documentation for 3.12 states

Normally [the number] field will be an integer or an integer range, but in certain cases it may also contain “S1”, “Suppl. 1”, in these cases the output should be scrutinised carefully.

While for issue it reads

The placement of issue is similar to month and number, integer ranges and short designators are better written to the number field.

issue still makes sense for more verbose identifiers such as "Spring"/"Summer" or "Michaelmas term".

Starting from version 5.0.111 BBT exports integer ranges and a few other short designators to number as well, see https://github.com/retorquere/zotero-better-bibtex/issues/925. This gives the expected output in your case.

So you'll now get

@article{John1996,
  title        = {A Nice Title},
  volume       = {10},
  number       = {2-3},
  journaltitle = {Annual Review of Something},
  date         = {1996},
  author       = {John, John}
}

which will yield

John, John. “A Nice Title”. In: Annual Review of Something 10.2-3 (1996).