Two footnotemarks in a tcolorbox yield footnotes with the same label

Question

To get the footnotes at the bottom of the page rather than at the bottom of the tcolorbox, I use \footnotemark inside the tcolorbox and \footnotetext below the tcolorbox. Here is a MWE:

\documentclass[11pt]{book}
\usepackage{tcolorbox}

\begin{document}
\begin{tcolorbox}
This is a \textbf{tcolorbox}\footnotemark.

And this is some text.\footnotemark. 
\end{tcolorbox}
\footnotetext{This is footnote 1}
\footnotetext{This is footnote 2}
And more text.\footnote{This is footnote 3}
\end{document}

and here is the output: (I had to fake it a bit in order to keep the size of the picture reasonable.):

Note that, at the bottom of the page, Footnote 2 and Footnote 3 are both labelled correctly as 2 and 3 while Footnote 1 is incorrectly labelled 2.

Answer 1

The cause for this problem has nothing to with tcolorbox -- \footnotetext uses \@thefnmark which is overwritten each time \footnotemark is applied, so multiple calls of \footnotemark will increase the footnote counter but there is no association of those footnote counter values with the corresponding \footnotetext. Multiple specifications of \footnotetext do not increase the relevant footnote counter label.

It is possible to use \footnotetext[value]{...} instead, which sets the footnote counter in a group -- it will not leak outside.

The solution below tracks the number of \footnotemark calls and assigns a label to it, \morefootnotetext retrieves the label and extracts the counter value, being typeset then with \footnotetext[value]{...}.

This approach will fail if there are more \footnotetext calls than \footnotemark assignments!

\documentclass[11pt]{book}
\usepackage{xassoccnt}
\usepackage{tcolorbox}
\usepackage{refcount}

\newcounter{totalfootnotes}
\newcounter{totalfootnotetexts}

\DeclareAssociatedCounters{footnote}{totalfootnotes}% Count all footnotes

\usepackage{xpatch}
\usepackage{xparse}
\xpatchcmd{\footnotemark}{\stepcounter}{\refstepcounter}{}{}
\xapptocmd{\footnotemark}{\label{fnmark-\number\value{totalfootnotes}}}{}{}
\xpretocmd{\footnote}{\stepcounter{totalfootnotetexts}}{}{}% Explicitly step!


\NewDocumentCommand{\morefootnotetext}{o+m}{%
  \IfValueTF{#1}{%
    \footnotetext[#1]{#2}%
  }{%
    \stepcounter{totalfootnotetexts}%
    \footnotetext[\getrefnumber{fnmark-\number\value{totalfootnotetexts}}]{#2}
  }%
}


\begin{document}
\begin{tcolorbox}
This is a \textbf{tcolorbox}\footnotemark

And this is some text.\footnotemark
\end{tcolorbox}
\morefootnotetext{This is footnote 1 from inside}
\morefootnotetext{This is footnote 2 from inside}
And more text.\footnote{This is footnote 3 from outside}

Now an example with 4 footnotemark\footnote{A dummy footnote} calls
\begin{tcolorbox}
This is a \textbf{tcolorbox}\footnotemark

And this is some text.\footnotemark

Stuff\footnotemark Otherstuff\footnotemark
\end{tcolorbox}
\morefootnotetext{This is footnote 3 from inside}
\morefootnotetext{This is footnote 4 from inside}
\morefootnotetext{This is footnote 5 from inside}
\morefootnotetext{This is footnote 6 from inside}

\end{document}