The story so far
Let us revisit how we developed our Fibonacci generator. When we created the app/controllers/views/fibonacci-help-main.wtf file, we were implicitly creating the content of the main page section for the /fibonacci/help URL. The naming convention should be obvious. Since no other page sections were defined at the time, the main section took up the entire web page.
We could similarly have created a file app/controllers/views/fibonacci-help-header.wtf to contain the header page section. However, we want a common header to be shared among all the pages for the Fibonacci generator so we made use of Woof!'s facility for inheriting templates by instead creating the file app/controllers/views/fibonacci-header.wtf which will be used as the header for any page within the Fibonacci URL tree that does not have its own page header defined.