Because every publication object has publisher and publisher= methods (thanks to attr_accessor :publisher), every magazine object has those methods too. In addition, magazine objects have editor and editor= methods:

Ruby sees all data structures and values—from simple scalar (atomic) values like integers and strings, to complex data structures like arrays—as objects. Every object is capable of understanding a certain set of messages. Each message that an object understands corresponds directly to a method—a named, executable routine whose execution the object

You learned in chapter 3 that if you define a method twice inside the same class, the second definition takes precedence over the first. The same is true of modules.