It was a little unclear to me if this question was asking me:
- To code up a UI extension and then document it? It seemed to me that this wouldn't be what you're looking for, but to be safe, I tried to split the difference and include at least some files that would be present in an extension, even if there is no real logic/code in them).
- To write a guide to creating UI Extensions in general, using an imaginary UI extension I've thought up as the example which will be used in the more general guide? I imagine this as more of a blog or tutorial type piece: i.e. "Today on the Contentful blog, I will show you how you can come up with your own UI extension for our web app, by walking you through how I created custom extension XYZ." This seemed the least likely to me given the phrasing of the question, so I decided not to go this route.
- To write documentation for a hypothetical extension, without real code for it. The way I read the question, this seems the most likely. I decided to not pick a specific functionality for the extension, only because I got hung up thinking about what would be a great idea (which isn't really the point of this assignment) and it was distracting me from actually writing the technical information about installing and such. That's why this tool is called "Thing" and why there are some placeholder []s. This way, you can also more clearly to see how I think structurally about writing docs than if I had written some actual content here.