The value of this environment variable must be a non-negative integer. The behavior of the program is implementation defined if the requested value of OMP_MAX_ACTIVE_LEVELS is greater than the maximum number of nested active parallel levels an implementation can support, or if the value is not a non-negative integer.
Since the second sentence states that the behavior is implementation defined if the value of OMP_MAX_ACTIVE_LEVELS is a non-negative integer, I suggest removing the first sentence, which restricts it from having such a value, or remove "non-negative" if the intent of the first sentence was to restrict it to an integral value.