Why ProblemDetails class has additional 's' in its name?

[NiceStepUp]

We have a debate about whether it is appropriate to have s or plural names in a class name. So as a guidance we took a look at ProblemDetails class which has s.

According to this msdn docs and if I understood this doc correctly, then name should be ProblemDetail, not ProblemDetails.

Can anybody explain to me why s is introduced there? I just want to keep to the best practice

[gfoidl]

is appropriate to have s or plural names in a class name

It's appropriate if the class represents something that is in plural. So why not?
For example look at https://grep.app/search?q=class%20%5Cw%2Bs%20&regexp=true&filter[lang][0]=C%23 which shows quite some class names ending with s.
That search also shows a basic .NET type -- especially in the event based world -- EventArgs with a plural name (as it can have more than one actual args).

I think ProblemDetails is correct, as it shows the details of the problem, which can be more than one -- so plural.

But note: naming is one of the hardest problem in software 😉
So choose a name that suits best your needs, and don't stick too hard to generic rules. When you're working in a team, maybe within the team you can determine your own rules that are followed along.