nag l2tabu caption/label checking versus \subcaptionbox

Question

The nag package used with the l2tabu option complains when \label is used in a float without following a \caption. Unfortunately, it does not understand that the first argument of \subcaptionbox from the subcaption package is a caption. It therefore complains here when it should not:

\RequirePackage[l2tabu]{nag}
\documentclass{article}
\usepackage{subcaption}

\begin{document}
\begin{figure}
  \subcaptionbox{Subfigure caption\label{example}}{subfigure content}
  \caption{Main figure caption}
\end{figure}
\end{document}

Sample output:

Package nag Warning: \label in float, but not after \caption on input line 7.

(Warning repeats four times.)

Any suggestions on how I can teach nag that \subcaptionbox creates a caption, and therefore that \label should be allowed here?

Answer 1

One could use this very dirty hack to satisfy the nag package:

\RequirePackage[l2tabu]{nag}
\documentclass{article}
\usepackage{subcaption}

\makeatletter
\let\subcaptionboxORI\subcaptionbox
\renewcommand\subcaptionbox{%
  \csname nag@hascaptiontrue\endcsname
  \subcaptionboxORI}
\makeatother

\begin{document}
\begin{figure}
  \captionbox{Subfigure caption\label{example}}{subfigure content}
  \caption{Main figure caption}
\end{figure}
\end{document}

Unfortunately this has an unwanted side-effect: The internal flag of the nag package will now be set by \captionbox*, which does not create a reference for \label, too. This is wrong.

So a better solution is updating to version 3.3 of the caption package. This version is available now and it contains an adaption to the nag package.