Inexpensive/generic checks first.
Sharing check is mostly for information-gathering right now.

It might not be a way to filter out windows in the future, but for now
it's the most flexible option.
Always be deleting/refactoring code.
Mouse moved events stop working when you close the first window in the list using ⌥W.
Oh yeah, by the way: ⌥W can be used to close windows.
Animate active status of thumanails.
BailUnless incurs DebugBreak, so switch their use in NNWindowFiltering.
Support for indexed subscripting in the HUD collection view
Share the Switch scheme and disable autoscheming.