Trying to modify multiaudience environment

Question

I'm using the multiaudience package - works pretty nice. Here is an example

\usepackage{multiaudience}
\SetNewAudience{internGER}
\SetNewAudience{externGER}
\DefCurrentAudience{internGER}
...
\begin{shownto}{internGER, externGER}
text for everyone
\begin{shownto}{internGER}
text for internals only
\end{shownto}
\end{shownto}

Now I would love to create an extra-option, that allows me to "mark" (text in red or underline or something like this) the internal text. That will make text-approval much easier, as you do not have to check both documents, but only one.

So I tried to recreate the shownto environment

  \let\oldshownto\shownto
  \let\endoldshownto\endshownto
  \renewenvironment{shownto}[1][]{%
  THIS TEXT WILL BE VISIBLE TO #1 :\\
 \oldshownto
  }{ %
  END OF VISIBLE TEXT\\
  \endoldshownto
  }

my plan was to use some "if-magic" based on argument #1, unfortunately there is no content in #1. What is wrong with this?

Here is the full minimal example - its compiling

\documentclass{article}
\usepackage{multiaudience}
\SetNewAudience{internGER}
\SetNewAudience{externGER}
\DefCurrentAudience{internGER}
%\DefCurrentAudience{externGER}
\let\oldshownto\shownto
\let\endoldshownto\endshownto
\renewenvironment{shownto}[1][]{%
-THIS TEXT WILL BE VISIBLE TO #1-, 
\oldshownto
}{ %
-END-\
\endoldshownto
}
\begin{document}
\begin{shownto}{internGER, externGER}
text for everyone.
\begin{shownto}{internGER}
text for internals only
\end{shownto}
\end{shownto}
\end{document}

Thanks Georg

Answer 1

You are defining the environment to take an optional argument, which by default is empty, but you want (1) the environment to take a mandatory argument, and (2) to pass this argument to the original environment.

However, the {shownto} environment is defined by \NewEnviron (in a way which makes me think that the author kind of misunderstood its usage...), so I'd take a different approach:

\documentclass{article}
\usepackage{multiaudience}
\SetNewAudience{internGER}
\SetNewAudience{externGER}
\DefCurrentAudience{internGER}
%\DefCurrentAudience{externGER}
% original definition
%\NewEnviron{shownto}[1]{%
%  @MULTAU@shownfalse@MULTAU@includetrue
%  \setkeys{MULTAU}{#1}%
%  \if@MULTAU@shown\BODY\fi}
\makeatletter
\RenewEnviron{shownto}[1]{%
   @MULTAU@shownfalse@MULTAU@includetrue
   \setkeys{MULTAU}{#1}%
   \if@MULTAU@shown
   [START TEXT SHOWN TO #1]%
   \BODY
   [END]%
   \fi
}
\makeatother
\begin{document}
\begin{shownto}{internGER, externGER}
text for everyone.
\begin{shownto}{internGER}
text for internals only
\end{shownto}
\end{shownto}
\end{document}