KVC simple path vs compound path

Hi
According to Apple's article about KVC http://developer.apple.com/document.../KeyValueCoding/Concepts/BasicPrinciples.html paths for valueForKey can be compound. I mean consist from several property names separated by dot.
So if I want to get value of property of an object inside of one of it's accessors, than I can use

Code:

[self.someproperty valueForKey:@"somevalue"];

or

Code:

[self valueForKey:@"someproperty.somevalue"];

But second does not work! It says "this class is not key value coding-compliant for the key". So what is the problem with compound key path?