Outline pages have trees of topics in an outline format, which in turn are linked to further outlines and articles providing more detail. Outlines show how important subtopics relate to each other based on how they are arranged in the tree, and they are useful as a more condensed, non-prose alternative to overview articles

together with martins, form a family of passerine birds known as the Hirundinidae. They are found around the world on all continents, including occasionally in Antarctica. There are around 90 species of Hirundinidae, with the greatest diversity found in Africa,

It is automatically generated from category tags at the bottoms of articles and most other pages. Nearly all of the articles available so far on the website can be found through these subject indexes.