Enforce Full Stop at the end of each Hanging Caption

Question

I am trying to enforce a full stop at the end of each caption in my LaTeX document. I found this post with basically the same question, but it breaks when using \usepackage{caption} as well as hanging captions.

So my goal is to

1. Append "." after each caption (when it doesn't already end with a full stop)
2. Make it work with hanging captions

I tried different things like redefining the \caption command. The closest I could get was by copy-pasting the original hang caption declaration from gitlab and adding the fullstop manually. Note that I'm using "ABC" to emphasise it even further - at the end I can simply replace that with \@addpunkt{.}. The issue with this solution is, that it writes the "ABC" into a new line which is of course not what I am looking for.

\usepackage{caption} % Use Caption Package
\usepackage{amsthm} % Adds a fullstop at the end of each caption automatically (if there is none)
\makeatletter
% Copied and adapted from "https://gitlab.com/axelsommerfeldt/caption/-/blob/master/source/caption3.dtx"
% Custom caption format based on the original hang format with "ABC" appended
\DeclareCaptionFormat{customhang}{%
  \caption@iflabelseparatorwithnewline
    {\caption@Error{%
       The option labelsep=\caption@labelsep@name' does not work\MessageBreak withformat=customhang'}}%
    {@hangfrom{#1#2}%
     \advance\caption@parindent\hangindent\relax
     \advance\caption@hangindent\hangindent\relax
     \caption@@par#3ABC\par}} % "ABC" is just a placeholder for "@addpunct{.}"
\makeatother
\captionsetup{format=customhang}

Here's a minimal example:

\documentclass{article}
\usepackage{graphicx} % Necessary if you are dealing with figures
\usepackage{amsthm} % Adds a fullstop at the end of each caption automatically (if there is none)
\usepackage{caption} % Use Caption Package
\usepackage{xltabular}  % For captions within xltabular testing
\makeatletter
% Custom caption format based on the original hang format with "ABC" appended
\DeclareCaptionFormat{customhang}{%
  \caption@iflabelseparatorwithnewline
    {\caption@Error{%
       The option labelsep=\caption@labelsep@name' does not work\MessageBreak withformat=customhang'}}%
    {@hangfrom{#1#2}%
     \advance\caption@parindent\hangindent\relax
     \advance\caption@hangindent\hangindent\relax
     \caption@@par#3ABC\par}} % "ABC" is just a placeholder for "@addpunct{.}"
\makeatother
\captionsetup{format=customhang}
\begin{document}
\begin{figure}
    \centering
    \caption{This is an example caption}
    \caption{Another sample with a very long caption and we hope that it will properly break into the next line with proper hanging...}
\end{figure}

Do you have any suggestions, or can I maybe achieve this even simpler? Thanks

Answer 1

The main problem is that #3 in \DeclareCaptionFormat refers to a quite complicated set of tokens that contains the caption text, but embedded in several commands.

My suggestion is to redefine \caption to pass a final \@addpunct{.}.

\documentclass{article}
\usepackage{graphicx} % Necessary if you are dealing with figures
\usepackage{amsthm} % Adds a fullstop at the end of each caption automatically (if there is none)
\usepackage{caption} % Use Caption Package
\makeatletter
% Custom caption format based on the original hang format with "ABC" appended
\DeclareCaptionFormat{customhang}{%
  \caption@iflabelseparatorwithnewline
    {\caption@Error{%
       The option labelsep=\caption@labelsep@name' does not work\MessageBreak withformat=customhang'}}%
    {@hangfrom{#1#2}%
     \advance\caption@parindent\hangindent\relax
     \advance\caption@hangindent\hangindent\relax
     \caption@@par#3}}
\NewDocumentCommand{\HIGHNOONcaption}{sO{#3}m}{%
  \IfBooleanTF{#1}{%
    \CAPTIONcaption*[#2@addpunct{.}]{#3@addpunct{.}}%
  }{%
    \CAPTIONcaption[#2@addpunct{.}]{#3@addpunct{.}}%
  }%
}
\makeatother
\captionsetup{format=customhang}
\AtBeginDocument{%
  \NewCommandCopy\CAPTIONcaption\caption
  \RenewCommandCopy\caption\HIGHNOONcaption
}
\begin{document}
\begin{figure}
    \centering
    %\includegraphics{example-image} % we don't really need it for the example
    \caption{This is an example caption}
    \caption{Another sample with a very long caption and we hope 
      that it will properly break into the next line with proper hanging.}
    \caption{Another sample with a very long caption and we hope 
      that it will properly break into the next line with proper hanging\dots}
    \caption{Another sample with a very long caption and we hope 
      that it will properly break into the next line with proper hanging?}
\end{figure}
\end{document}