What does "except that a default constructed array is not empty" mean?

In N3337, I'm reading §23.3.2.1/3 it states:

An array satisfies all of the requirements of a container and of a reversible container (23.2), except that a default constructed array object is not empty and that swap does not have constant complexity.

In §23.2.1, Table 96 Container Requirements, it shows a default constructed object X u; where the post condition is u.empty(). Presumably then, the following:

std::array<int, 0> a;

should result with a.empty() outputting 1, which it does. So what does "empty" mean here?