In swift, we use Filemanager.default.url(for:in:) to get user directories or system directories. And we pass arguments typed SearchPathDirectory and SearchPathDomainMask to specify what urls we need.
My question is the symbol of second parameter's type contains the word "mask" but I have no idea of what it actually hide. The actual work seems like "a group of directories' or 'what domain directories belong to".
I have no problem with actual programming with it but it just makes me curious.