One of the most common HTML constructs are lists (ordered or unordered), and any web application ends up having many of them, either for listing items or for components that do not even look like lists but for the purposes of marking up; an ul or ol fits the bill best. Luckily, Drupal has always had the item_list theme hook, which is flexible enough to allow us to use it in almost all cases.
The item_list theme hook is defined inside drupal_common_theme(), is preprocessed (by default) in template_preprocess_item_list(), uses the item-list.html.twig template by default, and has no default theme hook suggestions (because it's so generic and registered outside the context of any business logic). If we inspect its definition, we'll note ...
