How to use biblatex chapter+?

Question

If you allow me, I'll start with with a (not so) minimum example from biblatex: segmented bibliography with name of chapter which uses refsegment=chapter of biblatex and will do the slight change of adding the plus sign to the option refsegment=chapter+.

\documentclass{memoir}
\usepackage{lipsum}

\usepackage[american]{babel}
\usepackage[utf8]{inputenc}
\usepackage{csquotes}

\makeatletter
\renewcommand{\@chapapp}{Segment}
\makeatother

\usepackage{nameref}  

\usepackage[T1]{fontenc}
\usepackage[
    backend=biber,
    %bibencoding=utf8,
    % refsection=chapter,
    refsegment=chapter+,
    url=false,
    sorting=none,
    sortcites=true,
    sorting=nyt,
    style=apa
    %style=numeric
]{biblatex}
\DeclareLanguageMapping{american}{american-apa}

\makeatletter
%\newcommand*{\currentname}{\@currentlabelname}
\makeatother


% segmented bibliography
\defbibheading{subbibliography}{\subsection*{References for  Segment~\ref{refsegment:\therefsection\therefsegment}: \nameref{refsegment:\therefsection\therefsegment} }}

\DefineBibliographyStrings{english}{%
  references = {Works Cited},
}

\addbibresource{biblatex-examples.bib}

\usepackage[]{hyperref}
\hypersetup{
    colorlinks=false,
}


\begin{document}

\author{John Doe}
\title{Bla bla}

\tableofcontents

\chapter{First, there was light}
% \label{chapter1}

\lipsum[0-1]
Cite an author not previously cited~\cite{cicero}.
Note: Alphabetcially, K comes before S.

\section{A Section}

\lipsum[0-1]
Cite an author not previously cited~\cite{cicero}.
Note: Alphabetcially, K comes before S.

\chapter{Then, there was a power outage}
% \label{chapter2}

\lipsum[0-1]
And then again cite some authoprs cited previously~\cite{kastenholz}.
At vero eos et accusam et justo duo dolores et ea rebum~\cite{sigfridsson}.

\printbibheading
% \bibbysection[heading=subbibliography]
\bibbysegment[heading=subbibliography]

\end{document}

Doing so I get the error:

(/usr/local/texlive/2018/texmf-dist/tex/latex/biblatex/biblatex.cfg)

! Package biblatex Error: Option 'refsegment=chapter+' invalid.

See the biblatex package documentation for explanation.
Type  H <return>  for immediate help.
 ...                                              

l.13809 \blx@processoptions

?

Why is that?

The chapter+ option is there on page 52 of biblatex document.

Answer 1

Following https://github.com/plk/biblatex/issues/773 and https://github.com/plk/biblatex/pull/809 extended values like chapter+ for the 'sectioning-valued' options were introduced in biblatex v3.12. If you are using an older version you should look into updating your system.

---

Note that in newer versions of biblarex and biblatex-apa you won't need \DeclareLanguageMapping{american}{american-apa} any more. Starting from biblatex-apa 7.5 and biblatex 3.8 (November 2017) the language mappings are applied automatically.

For proper APA style you want to replace sorting=none, sortcites=true, sorting=nyt, style=apa,

with the simple

style=apa,