nicematrix with fontspec

Question

Why don't the nicematrix and fontspec package play well together?

Here is a MWE:

\documentclass{article}

\usepackage{nicematrix}
\usepackage{fontspec}
\usepackage{lipsum}

\begin{document}
\lipsum*[1-3]
$\begin{pNiceMatrix}a&b\\0&0\end{pNiceMatrix}$
\end{document} 

When you comment out either the fontspec package or the nicematrix package (and the corresponding environment) the compilation runs fine. As is, if you put in a NiceMatrix environment, it still compiles, but throws the error LaTeX Error: Missing \begin{document}.

Answer 1

In the latest update of the nicematrix package there is a zero width space

U+feff ZERO WIDTH NO-BREAK SPACE

at the start of line 21 before the % this is clearly an error, you should report to the package author.

You can save a local copy of the file, deleting the line

% \iffalse meta-comment

and it will run without error