self test examples doubt

[dolly shah]

I have some doubts from the book HFSJ, chapter:10, self test examples 3, 9 & 15.
I don't understand the answers given in the book. Because they don't explain the answers. Can anyone please explain?
Also I have found some examples's topics are not in the book but they are in the specification. Do I need to read the spec?

[Christophe Verré]

Also I have found some examples's topics are not in the book but they are in the specification.

You have to read this tutorial on Dynamic Attributes.

Do I need to read the spec?

Not necessarily. But I'd recommend to refer to it as much as you can whenever you have any doubt, or whenever you want to know more about a certain topic.