The *.info.yml file is required to create any theme. It helps us to notify Drupal that a theme exists and provides information to the Appearance interface that a theme is available to be installed. We will be working with *.info.yml files when creating any theme, so let's look at the makeup of a basic example.info.yml file:

name: Example 
description: 'An Example theme.' 
type: theme 
package: Custom 
base theme: classy 
core: 8.x 
 
libraries: 
  - example/global-styling 
 
regions: 
  header: Header 
  primary_menu: 'Primary menu' 
  secondary_menu: 'Secondary menu' 
  breadcrumb: Breadcrumb 
  help: Help 
  highlighted: Highlighted 
  content: Content 
  sidebar_first: 'Left sidebar' 
  sidebar_second: 'Right sidebar' 
  footer: Footer 
  page_top: 'Page top' 
  page_bottom: 'Page bottom' 

At first glance, the example.info.yml file is logical in structure and syntax. Starting from the top and moving our way down, the file is broken down by different sections of metadata containing general information, libraries, and regions. This information is described using a key:value format. We will begin with understanding how basic metadata works.