In the Drush Configuration section of the official documentation it is said:
drush.yml files are discovered as below, in order of precedence:
- Drupal site folder (e.g. sites/{example.com}/drush.yml).
- sites/all/drush, WEBROOT/drush, or PROJECTROOT/drush.
- …
There you can see "WEBROOT" and "PROJECTROOT", but there’s no explanation on what they are. In the Drush code there’s no mention either apart from the configuration itself:
$ grep PROJECTROOT * -r drush/docs/using-drush-configuration.md:2. `sites/all/drush`, `WEBROOT/drush`, or `PROJECTROOT/drush`. $ grep WEBROOT * -r drush/docs/using-drush-configuration.md:2. `sites/all/drush`, `WEBROOT/drush`, or `PROJECTROOT/drush`.
How Drush determines the values of PROJECTROOT and WEBROOT?