Each engine has been assigned one or more tags. Place the mouse over the engine's icon or name to see a brief description of the engine followed by the list of tags assigned to the engine. Click on the engine's icon or name to run a query on the engine or show the engine's home page in a pop-up window as described in How To Search.
Tags are displayed in a parent-child hierarchy, with children shown below and indented to the right of the parent. But the hierarchy is not fixed, it develops as you click on the triangle icons. For example, if you click on the triangle in the Shopping tag line, Books shows as a child of Shopping; but if you click on the Books triangle, Shopping shows as a child of Books. Clicking on a "closed" triangle (pointing to the right) in a tag's line will "open" the triangle (it will now point down) and show all tags that "co-occur" with the tag and its ancestors in the displayed hierarchy, where a set of tags are said to "co-occur" if there exists at least one engine tagged by all of them. The triangle will be invisible if there are no tags to show.
Clicking on a closed folder in a tag's line will open the folder and show all the engines that are tagged by the tag and its ancestors in the displayed hierarchy. The number of such engines is shown next to the tag. The very first line in the engines panel shows a "pseudo-tag" called "(Untagged)" that is used to show or hide the engines that have been assigned no tags. The folder for the pseudo-tag will be open in the initial state of Noflail Search.