Classes

Prepare our Dependency Injection Container
Log PHP errors to the Drush log. This is in effect until Drupal's error handler takes over.
The RedispatchHook is installed as an init hook that runs before all commands. If the commandline contains an alias or a site specification that points at a remote machine, then we will stop execution of the current command and instead run the command remotely.
Control the Drush runtime environment
Drush's shutdown handler
The TildeExpansionHook is installed as a preValidate hook that runs before all commands. Argument or option values containing a leading tilde will be expanded to an absolute path.

Interfaces

HandlerInterface represents a PHP system handler (e.g. the error reporting handler, the shutdown handler) that may be globally installed.