This Composer plugin will display a warning when users install Drupal packages that are not supported by the Drupal Security team, as per the Security Advisory Policy.
The relevant portion of the policy reads:
Security advisories are only made for issues affecting stable releases (Y.x-Z.0 or higher) in the supported major version branches (at the time of writing Drupal 7.x and Drupal 8.x). That means no security advisories for development releases (-dev), ALPHAs, BETAs or RCs.
Installing or updating a Drupal package with a dev, alpha, beta, or rc release will cause this warning to be displayed:
You are using Drupal packages that are not supported by the Drupal Security Team!
- drupal/memcache:dev-2.x
- drupal/conflict:1.0.0.0-alpha1
- drupal/multiversion:1.0.0.0-alpha12
- drupal/replication:1.0.0.0-alpha5
- drupal/workspace:1.0.0.0-alpha4
See https://www.drupal.org/security-advisory-policy for more information.