CLHS: Section 15.1.1.1

15.1.1.1 Array Indices

An array element is referred to by a (possibly empty) series of indices. The length of the series must equal the rank of the array. Each index must be a non-negative fixnum less than the corresponding array dimension. Array indexing is zero-origin.

The following X3J13 cleanup issue, not part of the specification, applies to this section:

ARRAY-DIMENSION-LIMIT-IMPLICATIONS:ALL-FIXNUM