@Override
    public List<ValidationEvent> validate(Model model) {
        List<ValidationEvent> events = new ArrayList<>();
        for (ServiceShape serviceShape : model.getServiceShapesWithTrait(EndpointRuleSetTrait.class)) {
            events.addAll(validateRuleSetAwsBuiltIns(serviceShape,
                    serviceShape.expectTrait(EndpointRuleSetTrait.class)
                            .getEndpointRuleSet()));
        }
        return events;
    }
Validator that AWS built-ins used in RuleSet parameters are supported.
smithy-aws-endpoints/src/main/java/software/amazon/smithy/rulesengine/aws/validators/RuleSetAwsBuiltInValidator.java