Conflict between `mbk` and `mwrep` and `newfloat`

Question

If I try to define a new float with:

\documentclass{mwart}
\usepackage{newfloat}
\DeclareFloatingEnvironment{plate}

It works.

But if I just change the class to

\documentclass{mwrep}
\usepackage{newfloat}
\DeclareFloatingEnvironment{plate}

I get this error message:

I get is error message:

line 6: Undefined control sequence. ...vironment[listname={List of plates}]{plate}
line 6: Missing \begin{document}. ...vironment[listname={List of plates}]{plate}
: Unsupported document class (or package) detected,(caption) usage of the caption package is not recommended.
: \caption will not be redefined since it's already(caption) redefined by a document class or package which is(caption) unknown to the caption package.

The same error happens if I use:

\usepackage{caption}

\DeclareCaptionType{plates}[Quadro][List of Plates]
\newenvironment{plate}{\captionsetup{type=plates}}{}

The book and report classes don't suffer from this problem at all. I tried to change the definition of caption to that of the default classes, but to no avail.

I know how to create a new float without a package with the mwcls classes, but the caption and newfloat packages are much more practical for that. Still, I have no idea what is causing this issue.

\documentclass{mwrep}
\usepackage{newfloat}
\usepackage[demo]{graphicx}
\usepackage{kantlipsum}
\DeclareFloatingEnvironment[listname={List of plates}]{plate}

\usepackage{caption}

\captionsetup{labelsep=endash}


\let\oldlistofplates\listofplates
\renewcommand{\listofplates}{
\begingroup%
    \let\oldnumberline\numberline%
    \renewcommand{\numberline}{Plate\ \oldnumberline}%
    \oldlistofplates%
\endgroup   

}

\begin{document}


\listoffigures
\listofplates


\section{A section}
\kant[1]
\begin{figure}[bp]
  \centering
  \includegraphics[width=2in]{fig}
  \caption{A figure}
\end{figure}
\kant[2]

\begin{plate}
  \centering
  \includegraphics[width=3in]{plate}
  \caption{A plate}
\end{plate}
\kant[3]
\end{document}

Answer 1

newfloat tests whether the class has chapters by looking at \@chapter; however the mwrep class doesn't define \@chapter like the standard classes do.

\documentclass{mwrep}

% mwrep has chapters, but does not define \@chapter
\makeatletter
\providecommand{\@chapter}{}
\makeatother

\usepackage{newfloat}
\usepackage[demo]{graphicx}
\usepackage{kantlipsum}
\DeclareFloatingEnvironment[listname={List of Plates}]{plate}

\let\oldlistofplates\listofplates
\renewcommand{\listofplates}{
\begingroup%
    \let\oldnumberline\numberline%
    \renewcommand{\numberline}{Plate\ \oldnumberline}%
    \oldlistofplates%
\endgroup   

}

\begin{document}


\listoffigures
\listofplates


\section{A section}
\kant[1]
\begin{figure}[bp]
  \centering
  \includegraphics[width=2in]{fig}
  \caption{A figure}
\end{figure}
\kant[2]

\begin{plate}
  \centering
  \includegraphics[width=3in]{plate}
  \caption{A plate}
\end{plate}
\kant[3]
\end{document}

Note that caption is not compatible with mwrep, so I removed it.