The struct is only named on the link you provided, not documented. So thanks for showing the absolute irony of it not being greatly documented, allowing people to misinterpret what it means.

Because it’s a boring enum in C, auto translated to a swift struct.

And if you’re reading the documentation because you do development, then you would already know that the header files are installed on your computer and you can trivially verify that there is nothing to document because it’s just a query key.