What is wrong with the following environment definition?

Question

I want to define an environment to hide text, with warning about it before and after in the pdf-output. What is wrong with the following definition?

\newenvironment{foldit}
{NB! NB! FOLDED TEXT BELOW\\ NB! NB! FOLDED TEXT BELOW\\ \iffalse}
{\fi ~~\\ NB! NB! FOLDEDTEXTABOVE \\ NB! NB! FOLDEDTEXTABOVE}

When I try to enclose some texts with \begin{foldit} .... \end{foldit}, I get the error message: Incomplete \iffalse; all text was ignored after line 105.

Answer 1

You might want to try package environ or comment:

\documentclass{article}
\usepackage{parskip}
\usepackage{comment}
\usepackage{environ}
\NewEnviron{foldit}{%
NB! NB! FOLDED TEXT BELOW\\
NB! NB! FOLDED TEXT BELOW\\
%\BODY
NB! NB! FOLDEDTEXTABOVE\\
NB! NB! FOLDEDTEXTABOVE\\
}
\NewEnviron{unfoldit}{%
NB! NB! FOLDED TEXT BELOW\
NB! NB! FOLDED TEXT BELOW\
\BODY\
NB! NB! FOLDEDTEXTABOVE\
NB! NB! FOLDEDTEXTABOVE\
}
\begin{document}
Line~1.
\begin{comment}
Line~2.
\end{comment}
Line~3.
\begin{foldit}
Line~4.
\end{foldit}
\begin{unfoldit}
Line~5.
\end{unfoldit}
\end{document}

Answer 2

Consider using environ to define foldit. It handles the environment definition in a similar way you'd expect from \newcommand, with the argument being \BODY - the body of the environment (between \begin{<env>}...\end{<env>}).

\documentclass{article}
\usepackage{environ,lipsum}
\NewEnviron{foldit}{%
  \par\noindent NB! NB! FOLDED TEXT BELOW
  \par\noindent NB! NB! FOLDED TEXT BELOW
  %\BODY
  \par\noindent NB! NB! FOLDED TEXT ABOVE
  \par\noindent NB! NB! FOLDED TEXT ABOVE
}
\begin{document}
1: \lipsum[1]
\begin{foldit}
2: \lipsum[1]
\end{foldit}
3: \lipsum[3]
\end{document}