FR: setting a labelprefix

[hu1buerger]

Proposal

I want to add a prefix to a enumeration such that the table can be rendered from - to - :

1. one one one 
2. two two two 
3. three three three
--- 
RQ-1: one one one 
RQ-2: two two two \label{rq2}
RQ-3: three three three

And intext the following
\autoref{rq2} is supported by the results. Magic two is two.

should compile to:
RQ-2 is supported by the results. Magic two is two.

What i know:

\item[RQ-2] can be used to replace the label, jet it would need manual intervention if the enumeration becomes reordered.

What i checked:

The documentation at ctan

What i tried:

\item[RQ-\theenumi.] two two two \label{rq2}

results in the enumeration to not advance

[SwitWu]

\documentclass{article}
\usepackage{enumitem}
\begin{document}
\begin{enumerate}[label=RQ-\arabic*:,ref=RQ-\arabic*]
  \item one one one
  \item two two two \label{rq2}
  \item three three three
\end{enumerate}

\ref{rq2} is supported by the results.

\end{document}

[manuelbb-upb]

In my document, I need this very often, e.g., prefixing with some theorem counter.
Additionally, the labels should have fancy formatting.
I ended up with a solution to reset some helper macro locally with the first* key.
The custom key prefix is defined using internals of enumitem, so it might break with future releases.
Also, I am fairly sure there are smarter ways than dealing with the expansion etc.
Compiled with LuaLaTeX on NixOS:

\documentclass[11pt,a4paper]{article}

\usepackage{enumitem}
\usepackage{csquotes}

% Define macro `\optionalPrefix`.
% If `\labelPrefix` is defined it is returned.
\ExplSyntaxOn
\NewExpandableDocumentCommand\optionalPrefix{}{%
    \cs_if_exist:cT { labelPrefix }%
    {{\use:c { labelPrefix }}.}%
}
\ExplSyntaxOff

% Define a new key `prefix` for list environments.
% It defines the `labelPrefix` locally in the list environment.
% We could also use `begin` and `after` instead of `first`,
% but would then have to use a group too.
\makeatletter
\enitkv@key{}{prefix}[]{%
    \enitkv@setkeys{enumitem}{%
        first*={\def\labelPrefix{#1}},%
    }%
}
\makeatother

\setlist[enumerate]{%
    align=left,
}

\setlist[enumerate,1]{%
    label=(\noexpand\optionalPrefix\arabic*),%
}
\setlist[enumerate,2]{%
    label=(\noexpand\optionalPrefix\arabic{enumi}.\roman*),%
}

\begin{document}

\noindent{}This is text before the enumerate environment, the prefix is \enquote{\optionalPrefix}.

\begin{enumerate}[prefix=TopPrefix]
    \item The \verb|prefix| is inherited by subenvironments:
    \begin{enumerate}
        \item This item should have \enquote{TopPrefix} in its label.
    \end{enumerate}
    \item For sublists, the prefix can be overriden:
    \begin{enumerate}[prefix=SubPrefix]
        \item This item should have \enquote{SubPrefix} in its label.
    \end{enumerate}
    The \verb|prefix| is kept alive by \verb|resume*|:
    \begin{enumerate}[resume*]
        \item \label{item:example} This item should still have \enquote{SubPrefix} in its label.
    \end{enumerate}
    The \verb|prefix| is reset by \verb|resume|
    \begin{enumerate}[resume]
        \item This item should have \enquote{TopPrefix} again.
    \end{enumerate}
\end{enumerate}

\noindent{}Outside of \verb|enumerate|, the prefix should be empty: \enquote{\optionalPrefix}.
The referenced item is~\ref{item:example}.

\begin{enumerate}
    \item Here, no prefix should be used.
\end{enumerate}

\end{document}

[hu1buerger]

Should this be PRed?