The goal of this feature is to simplify writing a set of validation constraints to be reused consistently across the application. Which is especially useful with DTOs, as a same set of constraints can be used in different places.

For instance, given multiple DTOs containing the new user password in for different use-cases (register, forgot pwd, change pwd), the same rules apply on the property. Hence with this PR, you can write a single constraint class to be reused:

/**
 * @Annotation
 */
class MatchesPasswordRequirements extends Compound
{
    protected function getConstraints(array $options): array
    {
        return [
            new NotBlank(),
            new Type('string'),
            new Length(['min' => 12]),
            new NotCompromisedPassword(),
        ];
    }
}

I'm open to better naming and ways to expose the options to the Compound::getConstraints method, so options can be forwarded to the nested constraints for most specific use-cases.