What files are ineligible for icloud drive?

Has Apple bothered to publish a reference that specifies:

1. what files are "ineligible" for iCloud drive?

2. what different icons associated with iCloud drive mean?

I just discovered that apparently files whose name end with a tilde are "ineligible" for iCloud drive. Given that people put their precious content and data on iCloud drive and pay for the service, shouldn't Apple clearly specifies what can and cannot be stored on iCloud drive?

Thanks