To get a list of all categories on the Tclers' Wiki, click on the title "Category Category" at the top of this page.
The top level for the category functionality of this Wiki.
One way to use this Wiki is to click on the title link of any page to get a list of all pages linking back to the current page. The category functionality is built on this mechanism. Links to category pages are intended to be placed on all Wiki pages. Users may then navigate to some category page, click on the "title link" for that page, and get a list of all pages "belonging" to that category.
To create a new category, create a new page representing the category, and place a link to the parent category on the page. There is a suggestion to name all category pages starting with the word, "Category", but this is not required, and many category pages do not do this. One reason is that many pages serve a dual purpose, both as category pages and as the primary content page for some topic.
Category links traditionally are placed at the bottom of a page, ordered from most-specific to least-specific, and using the <<categories>> wiki macro:
<<categories>> Sub Topic | Category
Which will be rendered similar to:
!!!!!! | [Category Sub Topic] | [Category Category] | !!!!!!
If necessary, the <<categories>> macro will prepend the word, "Category" to a page link to resolve it.
A category link on a page should answer the question, "What is this page about?", not the question, "What pages are about the same thing this page is about?". Answers to the latter should either be placed under a "See Also" heading on the page that the similar pages share as a common category, or simply be linked to the same category.
The page, How do Wiki Categories work contains a description of available categories. When adding a new category, please also add a description there.
See: http://emacswiki.org/ for a good example of how to use categories.
PYK 2013-09-03:
I am dubious of the value of special category pages because existing pages on each topic already exist, and creating separate pages that serve exclusively to earmark a thing as being a category is messy. For example, the page artificial intelligence exists, and is, by its existence and subject matter, already a category. The page Category AI, though, also exists, for no purpose other than as a node in a hierarchy of separate categories. The actual topic pages would work just as well for the purpose of categorizing things, and become category pages precisely when they are used as an argument to the <<categories>> feature. The advantages are that the category hierarchy can grow more naturally as real topics are added, that an almost reduntant set of special "category" pages need not be maintained, and it would be more straight-forward to add additional analytical functionality to the system based on the hierarchy that it could infer from the links and category links an a document.
The meta discussion at Tcl 2008 Conference Talks illustrates the mental gymnastics that a separate explicit set of category pages burdens Wiki users with.
I propose that to achieve the best results for this wiki, editors use the <<categories>> function of the wiki with first-class topic pages instead of category pages, and that we carefully curate pages to provide more substantial, organized, and readable content, even if it means duplicating some of the functionality that categories ostensibly provide. For example, I've started editing the Tcl 2008 Conference Talks to contain a set of links to individual conference presentations, even such a list could arguably be derived by using the "what links here" functionality of the wiki.
Given enough consensus, the time might even come when editors begin to actively dismantle pages named "Category ...".