Classes

The BootstrapHook is installed as an init hook that runs before all commands. If there is a @bootstrap annotation, then we will bootstrap Drupal to the requested phase.
This is a do-nothing 'Boot' class that is used when there is no site at --root, or when no root is specified.
Defines the available kernels that can be bootstrapped.

Interfaces

Defines the interface for a Boot classes. Any CMS that wishes to work with Drush should extend BaseBoot. If the CMS has a Drupal-Compatibility layer, then it should extend DrupalBoot.