Invalid HTML generated: unexpected end tag 'span' #40

Here is a minimal example:

\documentclass{article}

\begin{document}\small
\begin{enumerate}
  \renewcommand{\labelenumi}{(\arabic{enumi})}

\item An item.
\end{enumerate}
\end{document}

TeX is very user-friendly in this case by dropping all white-space
after the opening of the enumerate environment and
skipping over non-text generation code up to the first \item.

Found by xmllint.