Last modified: 2011-11-04 03:45:36 UTC
Almost all links in MediaWiki have a descriptive tooltip. Generally this is the page title, or an informationlet about the link. Subcategories in a category listing have no such tooltip. They should have something, even if it is just the page title prefixed with the localization of "Category:". Alternately, if you're a crazy byte-miser, you could wrap the descriptive <span> giving subcat/page/file count around both the category link and the number of subcats, but luckily nobody is that pedantic.
This is due to CategoryTree that subclass CategoryPage and CategoryViewer. If you go to http://en.wikipedia.org/wiki/Category:Cats?notree=1 you'll see that the tooltip appears correctly.
In addition to the sub-categories not including tooltips (title attr), the pages listed also dont include tooltips.