Are latitudes -90 and +90 both valid in WGS84?

Geometrically, I understand that a sphere can be addressed in latitude and longitude on the ranges [-90, +90] and (-inf, +inf) respectively.

However, I am working on the specification for plus codes, a geographic addressing system predicated on WGS84. So I am seeking a stronger normative reference than my intuition.

Does WGS84 have any limit on the range of allowable latitudes, and are the exact numbers -90 and +90 allowed (as distinct from "numbers approaching -90 and +90")?