Meaning of category delineations

Let's say I go to http://dmoz.org/Arts/Literature/

I'm a bit confused as to the semantics of the horizontal separators above the actual links. What are the three categories of links above "See Also?" I think it would help to add a small tag to each section (or TITLE hover text), because it is not very obvious to me.

Are the sections simply finer levels of granularity?

Thanks!
Kevin

They are all sub-categories (virtual sub-categories, though ontologically equivalent, being indicated with an @). Sometimes sub-categories divide into types. Here the middle set are types of literature, the last are things relating to literature, and the top I don't know how to describe. But they are different types of sub-category.

See-also are not sub-categories, though are related categories. A fine ontollogical distinction, but a sustainable one nonetheless.