rudimentary support for \begin{enumerate}[start=4] (enumitem package)

[eudoxos]

Please check this out, a sample document would be

\documentclass{article}
\usepackage{enumitem}
\begin{document}
	\begin{enumerate}[start=4]
		\item foo 
		\item bar
	\end{enumerate}
\end{document}

which renders (HTML5 only) correctly as

4. foo
5. bar

If you give it a green light, I would add unit tests, and support for some more enumitem options.

[eudoxos]

Where I need help: with \begin{enumitem}[label=\Roman*.,...], I need to get the label value before expansion, so that I can check whether it contains \Roman, \alph etc. Is it possible?

[eudoxos]

(The CI failure originates in this master commit: https://github.com/plastex/plastex/actions/runs/4247580725)