Implement bibliography string (formatting) classes (#555, #1027)

[moewew]

Inspired by #555, #1027, etc. This should make it easier to apply formatting to bibstrings. While it is tempting to just include formatting commands like \mkbibemph directly in the strings, it doesn't always yield best results as demonstrated in

\documentclass[french]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{babel}
\usepackage{csquotes}

\usepackage[style=authortitle-ibid, backend=biber]{biblatex}

\DefineBibliographyStrings{french}{
  andothers = {\mkbibemph{et\addabbrvspace al\adddot}},
  ibidem    = {\mkbibemph{ibid\adddot}},
}

\addbibresource{biblatex-examples.bib}

\begin{document}
Lorem \autocite{sigfridsson}
ipsum \autocite{sigfridsson}
dolor \autocite{aksin}
\printbibliography
\end{document}

The "ibid." in the second footnotes fails to be capitalised properly

2. ibid.

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With this commit we can define a new class for Latin terms and apply additional formatting (in the right place) only to those strings.

\documentclass[british,french]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{babel}
\usepackage{csquotes}

\usepackage[style=authortitle-ibid, backend=biber]{biblatex}

\DefineBibliographyStrings{french}{
  andothers = {et\addabbrvspace al\adddot},
  ibidem    = {ibid\adddot},
}

\DefineBibliographyExtras{french}{%
  \DeclareBibstringSet{latin}{andothers,ibidem}%
  \DeclareBibstringSetFormat{latin}{\mkbibemph{#1}}}

\UndefineBibliographyExtras{french}{%
  \UndeclareBibstringSet{latin}}

\addbibresource{biblatex-examples.bib}

\begin{document}
Lorem \autocite{sigfridsson}
ipsum \autocite{sigfridsson}
dolor \autocite{aksin}
\printbibliography

\selectlanguage{british}
Lorem \autocite{sigfridsson}
ipsum \autocite{sigfridsson}
dolor \autocite{aksin}
\printbibliography
\end{document}

---

This also helps with #899.

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@plk (and anyone else who wants to have a go) As always I don't feel particularly confident about the name. Suggestions are welcome. Other comments are of course also appreciated.

[plk]

I like the idea - if the "class" is only used to determine the format, how about just:

  \DeclareBibstringFormat{andothers,ibidem}{\mkbibemph{#1}}}

[moewew]

Good point. At least at the moment the classes are only for formatting. And I don't see much use apart from formatting.

The problem with

\DeclareBibstringFormat{andothers,ibidem}{\mkbibemph{#1}}}

would be that allowing a comma-separated list in the first argument would is inconsistent with \DeclareFieldFormat and friends.

If we have \DeclareBibstringFormat I'd also want a way to define format aliases (so that people can say ibidem and andothers are latin and latin is defined as ...). Normally the name for that is built by replacing Format with Alias (cf. \DeclareNameFormat - \DeclareNameAlias), this doesn't quite work here, I feel, since \DeclareBibstringAlias sounds like it does something different.

Plus there is the whole shenanigans about cleaning up after yourself, which needs some thoughts (currently via \UndeclareBibstringClass{...}). For that it appears to be easier to have a named object. Otherwise we'd have to list each string separately.

[plk]

How about:

\DeclareBibstringSet{latin}{...}
\DeclareBibstringFormat{latin}{...}

We already have "set" as a general concept in other places and it really is a set ... I don't think we need to say "SetFormat" as formats will only apply to sets and it'll be documented like that.

[moewew]

I like 'set'. fd333b1 hopefully changes all occurrences of 'class' to 'set'.

I chickened out of going for \DeclareBibstringFormat and went for \DeclareBibstringSetFormat to make it clear to users that we are formatting all bibstrings in a set and that \DeclareBibstringFormat can't natively be used to format a single bibstring. If you feel strongly about dropping the Set here, I can reconsider that decision.

[moewew]

Merged manually in e0816f1, 091ca1f, f9ed28e, 4579cca, 4348f30.