Question

The former is described in the KVC Prog Guide, but missing from iOS API installed with Xcode 4.0.2 (with iOS 4.3 SDK) for Snow Leopard which lists the latter.
This is for iOS 2.0 or newer. Thanks.

Answer 1

You can use both. For key named foo, you can either implement a specific method

-(BOOL)validateFoo:(id*)ioValue error:(NSError**)error {
        ...
}

or, a non-specific method

- (BOOL)validateValue:(id *)ioValue forKey:(NSString *)key error:(NSError **)outError {
      if([key isEqualToString:@"foo"]){
           ...
      }else{
          return [super validateValue:ioValue forKey:key error:outError];
      }
  }

It is perfectly sensible that you didn’t find validateIvar:error: in the API documentation, because the part Ivar needs to be changed for each key. You don’t find every method called setFoo: for keys foo you defined in the system API reference, do you?