OODA WIKI features 3 type of tooltips: inline tooltips added by editors, page preview tooltips for wikilinks, and reference tooltips.
Inline tooltips
Editors can add inline tooltips to articles using the {{Tooltip{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}}} template, like so: {{Tooltip|The text|The tool tip}} which makes it appear like this: The text.
The {{Abbr{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}}} template can be used for abbreviations. Tooltips are also used by various templates. For instance, the {{obsolete source{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}{{---}}}} template, here shown with a tooltip reason: [obsolete source].
In general, editors should use inline tooltips selectively such as when they're useful for table column headers. (See MOS:NOHOVER for information)
Editors should check that tooltip text renders as intended. For instance, if the tooltip text includes a " character, the tooltip is cut short.
Page Previews
When hovering over a link to another article, a short summary of the subject and an image (if available) is displayed as a tooltip.
Reference tooltips
When hovering over a reference, a tooltip appears that shows the full reference.