@Override
    public List<ValidationEvent> validate(Model model) {
        List<ValidationEvent> events = new ArrayList<>();

        for (Shape shape : new UnreferencedShapes(config.rootShapeSelector).compute(model)) {
            events.add(note(shape,
                    "This shape is unreferenced. It has no modeled connections to shapes "
                            + "that match the following selector: `" + config.rootShapeSelector + "`"));
        }

        return events;
    }
The Selector used to find root shapes, and any shape that is not connected to any of the returned root
shapes is considered unreferenced.

<p>Defaults to "service" if not set.

@return Returns the root selector;
smithy-model/src/main/java/software/amazon/smithy/model/validation/linters/UnreferencedShapeValidator.java