On several category pages (for example, CategoryReuse and CategoryBook), there are lists of pages that belong in those categories. Most of these pages have the appropriate category tags, as evidence by a click on the category title. This practice of listing pages seems to violate OnceAndOnlyOnce, and otherwise seems pointless since those pages can be accessed  by backlinks (and if they can't, they should be fixed!). The category pages could summarize the category by providing good examples and make the backlink search explicit.  This redundancy is most explicit on the MotherPage of all categories: CategoryCategory.

It has been the practice in the past to illustrate key pages which belong to the category, and the practice should not be discontinued or abolished. It also reduces the load on the server when people can use the available links on the page without resorting to the backlink feature. It also allows some commentary or guidance to be attached to the otherwise sterile and simple Backlinks file names. Some of the pages found by backlinks are not pages containing Category Material but are simply pages mentioning the Category name. It is not a violation of Once and only once, since to list the pages of the category on the page exercises the back link feature Once. This should be a Wiki which is easy and convenient to use. Five of the eleven principles (Incremental, Mundane, Unified, Organic, Convergent) are observed in the practice. See WikiDesignPrinciples.

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CategoryWikiMaintenance