Only it's not clear exactly where it's discussed. For instance, a search doesn't turn up the phrase "class object" anywhere before this sentence.

There's also a spelling error/typo in example code "declerations" should be "declarations".

The article (and the books) should go a lot further, building on what it's covered, showing more and more about how the pieces of the framework can fit together, or be glued together with over-rides, to make useful programs.