This is a set category. It should only contain pages that are {{{1}}} or lists of {{{1}}}, as well as subcategories containing those things (themselves set categories). Topics about {{{1}}} in general should be placed in relevant topic categories.
This is a maintenance category, used for the maintenance of BTW. It is not part of the encyclopedia and contains non-article pages, or groups articles by status rather than subject. Do not include this category in content categories.
Pages in this category should be moved to subcategories where applicable. This category may require frequent maintenance to avoid becoming too large. It should directly contain very few, if any, pages and should mainly contain subcategories.