decreased space before list with parbox=false following a section heading

[mbertucci47]

Sorry for adding to the list of issues with parbox=false, but I think with the fix for #262 a new issue has appeared. If a tcolorbox with parbox=false comes immediately after a section heading, then the space before a list that's preceded by text is decreased. Here's an example showing the issue:

\documentclass{article}
\usepackage{tcolorbox}

\begin{document}

\section{A section}

% too little space
\begin{tcolorbox}[parbox=false]
Some text
\begin{enumerate}
    \item First item 
    \item Second item 
\end{enumerate}
\end{tcolorbox}

% good
\begin{tcolorbox}[parbox=false]
Some text
\begin{enumerate}
    \item First item 
    \item Second item 
\end{enumerate}
\end{tcolorbox}

\subsection{A subsection}

% too little space
\begin{tcolorbox}[parbox=false]
Some text
\begin{enumerate}
    \item First item 
    \item Second item 
\end{enumerate}
\end{tcolorbox}

% good
\begin{tcolorbox}[parbox=false]
Some text
\begin{enumerate}
    \item First item 
    \item Second item 
\end{enumerate}
\end{tcolorbox}

% starting with a list is fine
\section{Another section}

\begin{tcolorbox}[parbox=false]
\begin{enumerate}
    \item First item 
    \item Second item 
\end{enumerate}
\end{tcolorbox}

\begin{tcolorbox}[parbox=false]
\begin{enumerate}
    \item First item 
    \item Second item 
\end{enumerate}
\end{tcolorbox}

\end{document}

There's no issue with boxes that start with a list.

[muzimuzhi]

Using overleaf (use \csname ver@tcolorbox.sty\endcsname to typeset version of tcolorbox),

• texlive 2023 (tcolorbox v6.0.4), reproducible
• texlive 2022 (tcolorbox v5.1.1), reproducible
• texlive 2021 (tcolorbox v4.51), not reproducible (the spacing above first list is still relatively narrower)
• texlive 2020 (tcolorbox v4.30), not reproducible (ibid)

[muzimuzhi]

I don't know why but prepending \let\if@nobreak\iffalse (which is the first assignment in \@arrayparboxrestore) to \tcb@parbox@false@settings seems to work.

Still need to find the "why part".

Example v2

```tex \documentclass{article} \usepackage[skins]{tcolorbox} \makeatletter \preto\tcb@parbox@false@settings{\let\if@nobreak\iffalse} \makeatother \newcommand\test[1][]{% \begin{tcolorbox}[#1, draft] Some text \begin{enumerate} \item First item \item Second item \end{enumerate} \end{tcolorbox} } \begin{document} LaTeX2e \fmtversion\par tcolorbox \csname ver@tcolorbox.sty\endcsname \section{parbox=false} \test[parbox=false] \test[parbox=false] \section{parbox=true} \test[parbox=true] \test[parbox=true] \end{document} ```

[T-F-S]

I don't know why but prepending \let\if@nobreak\iffalse (which is the first assignment in \@arrayparboxrestore) to \tcb@parbox@false@settings seems to work.

Still need to find the "why part".

I also wonder why the nobreak setting disturbs at this point.

Nevertheless, adding \let\if@nobreak\iffalse or \@nobreakfalse to \tcb@parbox@false@settings should do no harm and makes sense. If parbox=true is used, \if@nobreak equals \iffalse at begin of the tcolorbox interior of the MWE, but \iftrue for parbox=false.

So, I will add \@nobreakfalse to \tcb@parbox@false@settings.