abstract protected function build_header()
This is an abstract method that should be included in the theme-specific layout class that extends Method_Layout. In this method, you'll set up the header that appears on every page.
For layouts built inside the layout class, this method is called by the build_layout() method, which is called by build_page(). For layouts built directly inside the template, the markup for this method can be returned by using the get_header_markup() method. In either case, this method should not need to directly be called.
The build_footer() method does the same thing, but for the footer that appears at the bottom of every page. Trying to create a page for it causes GitHub to freak out and make it the footer of every wiki page.
This method accepts no arguments.
This method returns no value. Instead, markup for the header is added to the
$modals class properties.