WordPress has a templating system, which includes widgets that can be rearranged without editing PHP or HTML code, as well as themes that can be installed and switched between. The PHP and HTML code in themes can also be edited for more advanced customizations. WordPress also features integrated link management; a search engine-friendly, clean permalink structure; the ability to assign nested, multiple categories to articles; multiple author capability; and support for tagging of posts and articles. Automatic filters that provide for proper formatting and styling of text in articles (for example, converting regular quotes to smart quotes) are also included. WordPress also supports the Trackback and Pingback standards for displaying links to other sites that have themselves linked to a post or article. Finally, WordPress has a rich plugin architecture which allows users and developers to extend its functionality beyond the features that come as part of the base install.