A more graphical alternative to a single filter is at Special: CategoryTree. Search can also filter results by template names used, category membership, or pages linking to a specific page. Unlike most other filters, articletopic: also does page weighting: articles which are a stronger match for a topic will be higher in the search results (while articles which aren't about that subject at all will be removed from the result set completely). To get Wikipedia search results while on any web page, you can temporarily set your web browser's search box to become a Wikipedia search search box, even though you're on another web site (see Help:Searching from a web browser). Double quotes can define a single search term that contains spaces. Where spaces are significant: single search terms cannot have embedded spaces; work space, "work space", and workspace are all different. Search results will often be accompanied by a preliminary report. These will show off to the side of the page name, parenthetically. The order that search results are presented in is based on the page ranking software.
To power its search feature, Wikipedia uses CirrusSearch, a MediaWiki extension that uses Elasticsearch to provide enhanced search features. This trick removes the need to first navigate to Wikipedia from a web page, and then do the search or navigation.