We use a system of categories and sub-categories to help classify mblogs and their components. Think of it as a table of contents for all the mblogs and their components.
The sub-categories, sub-sub-categories, and so on are displayed as indented below the main category they belong to.
The + icons expand the sub-category branches while the - icons collapse them back down.
We allow up to 3 (sub)categories where mblogs may be cross-listed.