--- /dev/null
+<?php
+
+namespace Drupal\content_moderation\Plugin\Validation\Constraint;
+
+use Symfony\Component\Validator\Constraint;
+
+/**
+ * Verifies that nodes have a valid moderation state.
+ *
+ * @Constraint(
+ * id = "ModerationState",
+ * label = @Translation("Valid moderation state", context = "Validation")
+ * )
+ */
+class ModerationStateConstraint extends Constraint {
+
+ public $message = 'Invalid state transition from %from to %to';
+
+}