In Chapter 16 getting to documentation is covered, but I didn’t see reference to the use of the option key as an easy and fast way to get to the documentation for a objects like NSString.
If you hold down the OPTION key, and mouse over a keyword like NSDate or UIColor, the cursor turns to a question mark. If you click on the word while the ? is the cursor, a tiny help screen opens up. From the help screen, you can read the .h file, or, read the class documentation.
The ? option is not limited to just keywords, it even works on your own variables.
This is a very helpful and quick method to refresh or learn what’s behind the scenes.