Entity Validation API overview
In Drupal 8 Entity validation is moved to a separate Entity validation API and decoupled from form validation.
Defining Constraints (Validations) on Entities and/or Fields.
Constraints ensure data validity, integrity, and enforce business rules. They validate user input and display error messages.
Supported validation constraints [TBD]
List supported validation constraints and their settings.Also, document type-specific default constraints added in automatically here.