View source for Help:Categories

{{PD Help Page}}
Categories, a software feature of MediaWiki, provide automatic indexes that are useful as tables of contents.

You can categorize pages and files by adding one or more '''Category''' {{#ifeq:Category|{{ns:category}}||'''({{ns:category}})'''}} tags to the content text. These tags create links at the bottom of the page that take you to the list of all pages in that category, which makes it easy to browse related articles.

== Summary ==
Each of the pages in the '''Category''' [[Help:Namespaces|namespace]] represents a so-called '''category''', a grouping of related pages, and contains an index for the pages of its category. For example, this page belongs to "[[:Category:Help]]". If you open the "[[:Category:Help]]" page, you will see a link to this page there.

When a page belongs to one or more categories, these categories appear at the bottom of the page (or in the upper-right corner, depending on the [[Help:Preferences|skin]] being used).

The category pages themselves contain 2 parts :
* at their beginning, an optional part may contain text that can be edited, like any other page,
* at their end, an ever present, automatically generated, alphabetical list of all pages in that category, in the form of links. (In fact, in ASCII order. See [[Help:Special pages]]).

To assign a category to a page, simply add the link "<nowiki>[[</nowiki>Category:''Category name'']]" to the page's wikitext. The usual place to add it is at the bottom of the page.

To link a category page within a page as a normal wiki link (without adding the page to the category), prefix the link name with a colon.  For example: <nowiki>[[</nowiki>:Category:Not in this category]]

New categories can be [[Help:Starting a new page|created]] before assigning any page to it, in the same way as any other regular page.

Individual wikis may have their own top-level categories, such as [[wikipedia:Category:Contents|Category:Contents]] in Wikipedia.

For a complete list of all categories which have at least one page, see [[Special:Categories]].

For a complete list of all created/edited categories, including the ones that don't have any page, see [[Special:Allpages/Category:]] (note the colon at the end).

==Adding a page to a category==
To add a page or uploaded file to a category, simply edit the page and add the following text (where '''''Name''''' is the name of the category you want to add it to).

 <nowiki>[[</nowiki>{{ns:category}}:'''''Name''''']]

Any number of {{ns:category}} tags may be added to the page and the page will be listed in all of them. {{ns:category}} tags, along with [[mediawikiwiki:Manual:Interwiki#Interwiki_links_to_other_languages|interwiki language links]] placed in the sidebar, are usually added at the very bottom of the page for the convenience of other editors. 

On a categorised page, categories are displayed in the Categories: box strictly in the order they appear in the wikitext. 

If $wgUseCategoryBrowser is set to true, under the first list each category is listed again, [[wikipedia:breadcrumb (navigation)|breadcrumb]]-style, with all its parent categories, sorted alphabetically. (At least in MediaWiki 1.18.2) if a category is a subcategory of more than one parent, both hierarchies will be listed, but the tagged category will be stripped off all but one of these. This creates the potential for what appear to be duplicate entries if a category with multiple parents ''and'' one of its parents are both tagged on a page. For example suppose Maryanne is a subcategory of both Mary and Anne. If a page tags categories Maryanne and Anne then the Category breadcrumbs will show
 Anne 
 Anne
 Mary -> Maryanne

"Anne" appears to be duplicated, but what is meant is
 Anne 
 Anne -> Maryanne
 Mary -> Maryanne

This is probably a bug, and has been reported in [https://bugzilla.wikimedia.org/show_bug.cgi?id=33614 Bug 33614].

===Sort key===
By default, a page is sorted within a category under the first letter of its full name ''including the namespace''. Also, MediaWiki groups accented characters separately from their unaccented version, so pages starting by À, Á, Ä, will be listed under separate headings, instead of under heading A.

A ''sort key'' specifies under which letter heading, and where in the category list, the page will appear. You can add a sort key by placing it inside the tag after a pipe character. For example, the tag below will add the page under heading "S".

 <nowiki>[[</nowiki>{{ns:category}}:'''''Name'''''|'''''Sort''''']]

Sort keys are case-sensitive, and spaces and other characters are also valid. The order of the sections within a category follows the Unicode sort order. The sort key does not change the page title displayed in the category.

==Creating a category page==
Categories exist even if their page has not been created, but these categories are isolated from others and serve little purpose for organization or navigation.

A category is created by creating a page in the '''''Category:''''' namespace. A category page can be created the same way as other wiki pages (see [[Help:Starting a new page]]); just add "<code>{{ns:category}}:</code>" before the page title.

To avoid extra work, try searching within your wiki before creating a new category. The list of all categories can be found in "{{int:specialpages}}" in the "{{lcfirst:{{int:toolbox}}}}" box of the [[Help:Navigation#Sidebar|sidebar]].

Unlike other wiki pages, it is not possible to rename (move) a category. It is necessary to create a new category and change the {{ns:category}} tag on every page. The new category will not have the older category's page history, which is undesirable if there are many revisions.

==Managing the category hierarchy==   
Categories may belong to other categories in a hierarchy. Since category pages are much like any other page, a {{ns:category}} tag may be added to the bottom of a category page. 

It is a good idea to organize all categories into a hierarchy with a single top level category. The category structure can take the form of a tree with separate branches, but more often will have a graph structure. Generally, there should be a contiguous chain of parent-child links between each category and the top level category. 

==Hidden categories==
The categories that a page is in are normally listed at the bottom of the page. A category can be hidden from this list by adding the [[Help:Magic words|magic word]] "<code><nowiki>__HIDDENCAT__</nowiki></code>" to the category page. Hidden categories are not hidden from category pages ({{bugzilla|15550}}).

Users can choose to see hidden categories in a separate "{{int:hidden-categories}}" list, by checking "{{int:tog-showhiddencats}}" in the "{{int:prefs-rendering}}" section of [[Special:Preferences]].

Hidden categories are automatically added to [[:Category:{{mediawiki:hidden-category-category}}]]. This category is specified in the system message [[MediaWiki:Hidden-category-category]].

''See also:'' [[Help:Categories#Hidden_categories|hidden categories]]

==Linking to a category==
To create a link to a category, use a leading colon before the category name (without this colon, the current page would be added to the category):

:<code><nowiki>[[</nowiki>:{{ns:category}}:Help]]</code> &rarr; '''[[:{{ns:category}}:Help]]''' 

To change the link text, write the text inside the link tag after a pipe:

:<code><nowiki>[[</nowiki>:{{ns:category}}:Help|Help category]]</code> &rarr; '''[[:{{ns:category}}:Help|Help category]]'''
 
[[Help:Redirects|Redirect pages]] that redirect to categories must also use the colon, otherwise they will be added to the category instead of redirecting.

==Redirecting a category==
Like normal wiki pages, category pages can be redirected to other normal or category pages. ''However'', this is not recommended, as pages categorised in redirected categories do ''not'' get categorised in the target category ([https://bugzilla.wikimedia.org/show_bug.cgi?id=3311 bugzilla:3311]). Some Wikimedia sites use a "category redirect" template to mark redirected categories, allowing manual or automated cleanup of pages categorised there.

==Tracking Categories==
Certain syntax issues, such as a broken image link, or too many expensive parser functions, can cause a page to be added to a tracking category. See [[mediawikiwiki:Help:Tracking_categories|Help:Tracking categories]] for details.

==See also==
* [[mediawikiwiki:Category:Category_extensions|Category:Category extensions]]

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