The site structure and menus are built by a plug-in in site_structure.rb. This plug-in looks in the YAML front matter{:target=“_blank”} for child pages to build the structure, and breadcrumbs to determine the parent pages to display.
Child pages are a list of objects, stored in the field children. These are defined by string path to a file or a YAML object with a path to another file, or a link to an external URL. In addition a title can be defined for the text content of the HTML menu option. See the example below from /guide/index.md{:target=“_blank”}
{% highlight yaml %} breadcrumbs: