private List<ValidationEvent> validateRuleSetBuiltIns(ServiceShape serviceShape, EndpointRuleSet ruleSet) {
        List<ValidationEvent> events = new ArrayList<>();
        for (Parameter parameter : ruleSet.getParameters()) {
            if (parameter.isBuiltIn()) {
                validateBuiltIn(serviceShape, parameter.getBuiltIn().get(), parameter, "RuleSet")
                        .ifPresent(events::add);
            }
        }
        return events;
    }
Validates that the built-in's specified on parameters are supported.
smithy-rules-engine/src/main/java/software/amazon/smithy/rulesengine/validators/RuleSetBuiltInValidator.java