Adding NOT selections to checkbox interfaces

We've recently come across questions online and in our own work about how to deal with negative selections in a checkbox UI. Usually, a checkbox's on/off status in something like faceted nav is enough to convey that you're not interested in seeing results from the unselected items. But what if you specifically want to select items to exclude?

Grafting NOT functionality into a checkbox UI can make the UI feel overly complicated and unintuitive. But a couple days ago, quite by chance, I found a site that's doing it well.

I was searching for a knitting pattern on Ravelry, an online community for people interested in fiber arts. Ravelry's search uses a standard faceted UI to help narrow results:



Since I don't crochet, I clicked on "knitting" in the Craft box to limit the number of patterns. That's when this additional dropdown appeared:



I pulled it down to explore further:



Ravelry's use of simple Venn diagrams to convey what can be confusing search concepts to nontechnical users is a great idea, and using soft colors and a light gradient to help the dropdown feel friendly and accessible is also a smart choice. But I was especially pleased to see them take things one step further once you actually select an item in a NOT search:



Putting the "do not" icon in the checkbox reinforces the choice the user made from the dropdown, and makes it crystal-clear how search results will be affected.

For most Ravelry searches, you won't need this additional UI feature. But it's there if you do, and it's the best solution I've seen for this complicated problem.