New environment with content inside multicolumn

Question

I'm trying to create a new environment with arguments that puts the content inside a multicol like this

\begin{tabular}{p{5em} p{\textwidth-3\columnsep -5em}}\\[-0.5em]
\toprule \addlinespace[1.4ex]
\textbf{NFR-1} & \textbf{Extensibility} \hfill \textbf{P1} \\ \addlinespace
\midrule[\heavyrulewidth] \addlinespace[1.4ex] 
\multicolumn{2}{p{\textwidth-2\columnsep}}{Description text} \\ \addlinespace
\midrule \addlinespace
\end{tabular}\\[1em]

which becomes

When i setup the new environment as in this MWE

\documentclass{article}
\usepackage{booktabs,calc}
\usepackage{hyperref}

\newenvironment{card}[4]{
\hypertarget{#1:#2}{}
\vspace{0.75ex}
\centering
\setlength{\defaultaddspace}{1.2ex}
\begin{tabular}{p{5em} p{\textwidth-3\columnsep -5em}}\\[-0.5em]
\toprule \addlinespace[1.4ex]
\textbf{#1-#2} & \textbf{#3} \hfill \textbf{#4} \\ \addlinespace
\midrule[\heavyrulewidth] \addlinespace[1.4ex] 
\multicolumn{2}{p{\textwidth-2\columnsep}}
}{
\\ \addlinespace
\midrule \addlinespace
\end{tabular}\\ [1em]
}

\begin{document}
\begin{card}{NFR}{1}{Extensibility}{P1}
Description text.
\end{card}
\end{document}

it looks strange:

I think it doesnt like the splitup of the multicolumn command. I've already tried \bgroup and \egroup but that only produced errors.

What can be done in a situation like this?

Answer 1

Something like this?

environ provides a way of defining new environments such that you can process the entire contents of the environment, which it captures in a macro. By default, the contents is stored in \BODY, although you can customise this if necessary to avoid clashes (see manual, prooftrees.sty includes an example of how to do this to avoid clashing with forest.sty's usage of \BODY).

\documentclass{article}
\usepackage{booktabs,environ,calc}
\usepackage{hyperref}

\NewEnviron{card}[4]{%
  \hypertarget{#1:#2}{}%
  \vspace{0.75ex}%
  \centering
  \setlength{\defaultaddspace}{1.2ex}%
  \begin{tabular}{p{5em} p{\textwidth-3\tabcolsep-5em}}\\[-0.5em]
    \toprule \addlinespace[1.4ex]
    \textbf{#1-#2} & \textbf{#3} \hfill \textbf{#4} \\ \addlinespace
    \midrule[\heavyrulewidth] \addlinespace[1.4ex]
    \multicolumn{2}{p{\textwidth-2\columnsep}}{\BODY} \\ \addlinespace
    \midrule \addlinespace
  \end{tabular}%
  \vspace{1em}% you can't use \\ here and should never use it outside tabular etc. anyhow
}

\begin{document}
\noindent
\begin{card}{NFR}{1}{Extensibility}{P1}
  Description text.
\end{card}
\end{document}

Answer 2

You want a one column tabular:

\documentclass{article}
\usepackage{booktabs,calc}
\usepackage{hyperref}
\usepackage{lipsum}

\newenvironment{card}[4]{%
  \par\hypertarget{#1:#2}{}\vspace{0.75ex}
  \centering
  \setlength{\defaultaddspace}{1.2ex}
  \begin{tabular}{p{\textwidth-2\tabcolsep}}\\[-0.5em]
  \toprule
  \addlinespace[1.4ex]
  \makebox[5em][l]{\textbf{#1-#2}}\hspace{2\tabcolsep}\textbf{#3}\hfill\textbf{#4}\\
  \addlinespace
  \midrule[\heavyrulewidth] \addlinespace[1.4ex] 
}{%
  \\ \addlinespace
  \midrule \addlinespace
  \end{tabular}
  \par\vspace{1em}
}

\begin{document}

\lipsum[2]

\begin{card}{NFR}{1}{Extensibility}{P1}
Description text.
\end{card}

\lipsum[3]

\end{document}

The spacings seem not to obey any specific rule, though.

Note that the parameter for the intercolumn spaces is not \columnsep, but rather \tabcolsep (and each column has such space at either side).