Why doesn't Ior have a specific type for "warning" in Arrow-kt?

Question

Why does Ior have only two generic types as parameters?

Isn't this inconsistent with the benefits of typed errors, since a "warning" can be different from an "error"?

Doesn't this make "exhaustive when" confusing for error handling?

Would it be considered bad practice if the following code were possible?

sealed interface UsernameError {
    object TooShort : UsernameError
    object TooLarge : UsernameError
}

sealed interface UsernameWarning {
    object ShouldBeShorter : UsernameWarning
    object WithDeprecatedChar : UsernameWarning
}

@JvmInline
value class Username private constructor(val value: String) {
    companion object {
        fun create(value: String): Ior<UsernameError,UsernameWarning, Username> {
            return when {
                value.length < 8 -> UsernameError.TooShort.leftIor()
                value.length > 64 -> UsernameError.TooLarge.leftIor()
                value.length > 20 -> Pair(UsernameWarning.ShouldBeShorter, Username(value)).bothIor()
                value.contains('#') -> Pair(UsernameWarning.WithDeprecatedChar, Username(value)).bothIor()
                else -> Username(value).rightIor()
            }
        }
    }
}

I would like to understand the reason why the library does not allow this possibility.