The Categorizing templates/de-formal category contains templates that add one or more categories to an article.
It is recommended that these templates have a parameter that can be used to suppress the inclusion of the categories. This enables the use of the template in how to articles and other sorts of documentation without spurious inclusion of the host page in one or more categories. For examples of how to do this, please see Template:Extension/de-formal and Template:MediaWikiHook/de-formal.
Many templates in the Alert templates category also categorize.