The following MWE does not work as expected: It throws an error during compilation, despite the result seems to be correct. MWE:
\documentclass[11pt]{article} % use larger type; default would be 10pt
\usepackage[utf8]{inputenc} % set input encoding (not needed with XeLaTeX)
\usepackage{enumitem}
\title{Brief Article}
\author{The Author}
\begin{document}
\maketitle
\section{First section}
\begin{enumerate}
\item[i.] first item
\begin{enumerate}
\item nested item under first item
\end{enumerate}
\item[i + 1.] second item
\end{enumerate}
commentary
\begin{enumerate}[resume]
\begin{enumerate}[resume]
\item shall be nested item under second item
\end{enumerate}
\item[j] third item
\end{enumerate}
\end{document}
The thrown error's message is "Something wrong, perhaps a missing \item [at] l.24 \begin{enumerate}[resume]". But this message should not appear since I'm using enumitem.
The result seems (!) to be correct -- I don't know exactly because of a missing counter before the (a) in the second list (2.(a)):
Besides: How could I achieve a numbering (.() (i. e. 2.(a)?