This is a chronological category. Do not diffuse files from the main topic category into this category; instead, add them to this category while retaining them in the main topic category as well.
This category should only contain other categories. Galleries should be in the corresponding categories instead. Files should be in a parent or subcategory.
This flat category gathers all sub-categories with the criterion“by period” in its name (whether at the end or in the middle) in a non-hierarchical list.
This category is hidden and appears in the second line of categories. It is not shown if the appropriate user preference is deactivated.
See also: Category:Categories by style (flat list). 
