Without "arbitrary_precision" enabled, what can Value::Number be?

[JPRomer0]

So in the code(number.rs), when "arbitrary_precision" feature is enabled, this is the Number representation, it seems.

#[cfg(not(feature = "arbitrary_precision"))]
#[derive(Copy, Clone)]
enum N {
    PosInt(u64),
    /// Always less than zero.
    NegInt(i64),
    /// Always finite.
    Float(f64),
}

The question is, is it an API level gurantee that running one of:
is_u64()
is_i64()
is_f64()
will return true or is it just the case at the moment?