[Tex/LaTex] How to you set an enumerate counter which contains both letters and numbers

Question

I am including, using the enumerate environment, some sections from legislation.

In legislation, it is common to indicate subsections which were added later through the use of letters. So, for example, we might have:

5    Awesome section

(1)  This subsection existed from the beginning.
(1A) This subsection was inserted later.
(2)  And we continue with the original Act

I'm having trouble inserting '(1A)' as an enumerate counter.

When I use the enumerate package, and do:

\begin{enumerate}[(1A)]

the package appears to treat 'A' as the counter, and outputs '(AA)'.

When I try to use setcounter, as in:

\begin{enumerate}
    \setcounter{enumi}{1A}

I get

! Package calc Error: `A' invalid at this point.

How can I insert (1A), or similar letter number combinations, as an enumerate counter?

I'm not awfully fussed that it actually count correctly; I'm just after identical formatting to a normal enumerate environment.

Answer 1

This introduces a command \addeditem which uses itemtopnumber itemsubletter, i.e. 1A 1B etc. if necessary, however there is some 'bug' that the counter is not correctly advanced, I try to figure out why, so that one has to reset it manually at the moment.

\documentclass[paper=a4,12pt]{scrbook}

\newcounter{itemadded}
\setcounter{itemadded}{0}


\newcommand{\addeditem}{%
\addtocounter{enumi}{-1}%
\stepcounter{itemadded}
\let\LaTeXStandardLabelEnumi\labelenumi%
\renewcommand{\labelenumi}{\textbf{(\arabic{enumi}\Alph{itemadded})}}%
\item 
% Switch back to old labelling 
\let\labelenumi\LaTeXStandardLabelEnumi%
}%


\let\LaTeXStandardEnumerateBegin\enumerate
\let\LaTeXStandardEnumerateEnd\endenumerate

\renewenvironment{enumerate}{%
\LaTeXStandardEnumerateBegin%
\setcounter{itemadded}{0}
}{%
\LaTeXStandardEnumerateEnd%
}%


\begin{document}

\begin{enumerate}
\item First
\addeditem First added
\addeditem Second added
\item Next item 
\item Third item \setcounter{itemadded}{0}
\addeditem Another subitem added
\end{enumerate}


\begin{center}
\huge Just a repeat without resetting \texttt{itemadded}
\end{center}

\begin{enumerate}
\item First
\addeditem First added
\addeditem Second added
\item Next item 
\item Third item
\addeditem Another subitem added
\end{enumerate}


\end{document}