The page descriptor is required to register the page and allows us to set up user input fields to configure the page. It also allows us to describe what regions are available in this page.

  <display-name>My first page</display-name>
A simple human readable display name.
The config element is where input fields are defined for configurable data that may be used on the page.
This is where regions are defined. Various component parts can be dragged and dropped into regions on the page.