This template is used on 33,000+ pages and changes may be widely noticed. Test changes in the template's /sandbox or /testcases subpages, or in your own user subpage. Consider discussing changes on the talk page before implementing them.
This hook allows you to add up to ten optional categories, that will be added to a page if a particular parameter is defined. Each category will be added if the corresponding parameter is non-empty. This template displays no visible output, so it can be put anywhere in the template code; common practice is to put it attached to a task force hook, such as |TF_n_HOOK=.