Biblatex-sbl with first citation of something other than page number (footnote) for type article

Question

In some fields, it is preferable when citing a footnote in another work, to cite the page number with the footnote number. In biblatex-sbl, if this is the first citation of an article, then it sees the prenote as something other than a page number and puts the whole page range in the footnote and then the postnote in parenthesis, which is not correct.

Here is a MWE:

\documentclass[letterpaper,12pt]{book}
\usepackage{polyglossia}
\setmainlanguage[variant=us]{english}
\usepackage[english=american]{csquotes}

\begin{filecontents}[overwrite]{customstyles.dbx}
  \DeclareDatamodelEntrytypes{tdict}
\end{filecontents}

\usepackage[style=sbl,citepages=omit,fullbibrefs=true,sblfootnotes=false,citereset=chapter]{biblatex}

\begin{filecontents}[overwrite]{temp.bib}
@article{article1,
   title     = {First Article Title},
   author    = {John Smith},
   journal   = {Journal Title},
   volume    = {3},
   number    = {2},
   year      = {2020},
   pages     = {15-30},
}

@article{article2,
   title     = {Second Article Title},
   author    = {John Denver},
   journal   = {Journal Title},
   volume    = {3},
   number    = {2},
   year      = {2020},
   pages     = {31-45},
}

\end{filecontents}

\addbibresource{temp.bib}

\usepackage{xparse}

\begin{document}

\null\vfill
Cite a normal page.\footcite[18]{article1} Cite a footnote.\footcite[20fn2]{article1}
Now cite a footnote first.\footcite[35fn3]{article2}

\clearpage
\printbibliography%
\end{document}

Here is what it looks like:

If the first citation is a page number, and then the second citation includes something other than a page number, the short citation is correct.

However, if the first citation includes a reference to a footnote (so that the postnote contains something other than just numbers), the full reference is wrong.

Is there a way to get biblatex-sbl to treat this as a page number?

I did find this issue, but I am unsure what exactly to do. Do I need to manually define passifpages? It does not look like this command is natively defined in biblatex. And the comment about the definition of PagesCheckSetup having a trivial definition is also confusing because it looks like this command does have a definition in biblatex.

Answer 1

Here is how you could use \passifpages (as defined in https://github.com/plk/biblatex/issues/918#issuecomment-581051609). The command is not defined in the biblatex core, so you have to bring your own definition. The idea is that this command normally does nothing normally (\@firstofone defines a macro that returns its single argument), but that is defined to hide its argument when biblatex checks if something is a valid page range (that's what the \PagesCheckSetup does).

\documentclass[letterpaper,12pt]{book}
\usepackage{polyglossia}
\setmainlanguage[variant=us]{english}
\usepackage[english=american]{csquotes}

\usepackage[style=sbl,citepages=omit]{biblatex}

\makeatletter
\let\passifpages\@firstofone
\PagesCheckSetup{\let\passifpages\@gobble}
\makeatother

\addbibresource{biblatex-examples.bib}

\begin{document}
\null\vfill
Cite a normal page.\footcite[18]{sigfridsson}
Cite a footnote.\footcite[\passifpages{20fn2}]{sigfridsson}
Now cite a footnote first.\footcite[\passifpages{35fn3}]{aksin}

\clearpage
\printbibliography
\end{document}

If you cite many footnotes it might become tedious to always add \passifpages. There are two ways to make your life easier.

1. You can allow f and n as part of numbers with

   \documentclass[letterpaper,12pt]{book}
   \usepackage{polyglossia}
   \setmainlanguage[variant=us]{english}
   \usepackage[english=american]{csquotes}
   
   \usepackage[style=sbl,citepages=omit]{biblatex}
   
   \DeclareNumChars{nf}
   
   \addbibresource{biblatex-examples.bib}
   
   \begin{document}
   \null\vfill
   Cite a normal page.\footcite[18]{sigfridsson}
   Cite a footnote.\footcite[20fn2]{sigfridsson}
   Now cite a footnote first.\footcite[35fn3]{aksin}
   
   \clearpage
   \printbibliography
   \end{document}
   

   Technically this means that arguments such as nfffnnfnfn will now "count" as numbers, which is probably not too bad.

2. You can define a special command for fn<number>, say \fn that can again be hidden from the page checking code hidden.

   \documentclass[letterpaper,12pt]{book}
   \usepackage{polyglossia}
   \setmainlanguage[variant=us]{english}
   \usepackage[english=american]{csquotes}
   
   \usepackage[style=sbl,citepages=omit]{biblatex}
   
   \makeatletter
   \newcommand*{\fn}[1]{fn#1}
   \PagesCheckSetup{\let\fn\@gobble}
   \makeatother
   
   \addbibresource{biblatex-examples.bib}
   
   \begin{document}
   \null\vfill
   Cite a normal page.\footcite[18]{sigfridsson}
   Cite a footnote.\footcite[20\fn{2}]{sigfridsson}
   Now cite a footnote first.\footcite[35\fn{3}]{aksin}
   
   \clearpage
   \printbibliography
   \end{document}