private boolean isConstraintAnnotation(Annotation annotation) {
        return annotation.annotationType().isAnnotationPresent(Constraint.class);
    }
Check whether the given annotation is marked as {@link Constraint @Constraint} itself and may therefore hold additional validation annotations.

@param annotation annotation instance to check
@return whether the given annotation represents a constraint to consider during validation
jsonschema-module-javax-validation/src/main/java/com/github/victools/jsonschema/module/javax/validation/JavaxValidationModule.java