Q about xr.set_options and xr.open_mfdataset

[PythonSchlumpf]

Dear xarray experts,

I have to questions.

1. How does xr.set_options(warn_for_unclosed_files=True) work? When does it show a warning? Do you have an example for it, where I could see the warning, please?
2. xr.open_mfdataset: How can I ensure the files are closed properly after this function read the content of them, please?

Many thanks!