[plone.restapi] Including a custom endpoint for expansion mechanism

i have a custom Plone RestAPI endpoint @guideline and I want to make this endpoint available for the API expansion (?expands=guideline). Is this possible? Or what makes a component in order to appear under @components in a response?

You can follow the code that bobtemplates.plone generates, it creates the endpoint, it is expandable and appears in the @components section: