Actually, this circles us back to #493: if we can make a general-purpose way to negate any matcher, then you could just say:

``` ruby
expect(list).to all( not be_full )
```

...or whatever.  There's still the problem that `not` is a keyword, though.  But before adding a separate matcher for negation, I'd like to see if we can find a way to provide general purpose negation.