Why does valueForKey: on a UITextField throws an exception for UITextInputTraits properties?

Running this:

@try
{
    NSLog(@"1. autocapitalizationType = %d", [self.textField autocapitalizationType]);
    NSLog(@"2. autocapitalizationType = %@", [self.textField valueForKey:@"autocapitalizationType"]);
}
@catch (NSException *exception)
{
    NSLog(@"3. %@", exception);
}

Outputs this:

1. autocapitalizationType = 0
3. [<UITextField 0x6c15df0> valueForUndefinedKey:]: this class is not key value coding-compliant for the key autocapitalizationType.

I was expecting:

1. autocapitalizationType = 0
2. autocapitalizationType = 0

This exception only happens with properties that are part of the UITextInputTraits protocol. Regular properties of a UITextField such has clearButtonMode can be accessed through valueForKey:.

So why can't you access UITextInputTraits properties with key-value coding?