For the record, checked through past suggestions and found that the last time this came up was in 2021. Definitely time to pitch it again.

What functionality is missing? What is unsatisfying with the current situation?

Currently searching articles will only check the title, tags, ang vignette. This kind of screws over those of us who primarily use prompt boxes, and therefore, I would argue, subtly discourages the use of prompt boxes, which are one of my FAVORITE features. Furthermore, I was not aware long ago when I first started in WA that the prompt boxes were not searchable, and by the time I found that out, I was many, many articles in. I'm sure there are others that have had the same experience.  

How does this feature request address the current situation?

Allowing the Search to check through prompt boxes as well as the vignette would take away one of the major downsides of using prompt boxes. It also results in more thorough search results, and who doesn't want that?  

What are other uses for this feature request?

The search feature could even be expanded to take into account the sidebar. There's lots of linked information there that could be made much more useful if it created a searchable feature. Like searching "oligarchy" would pull up the governments with that selected.

Final thoughts: It has occured to me that you could simply create a subheading that matches the prompt box's in your vignette, put your content there, and that would make it searchable, but I would like to point out that this suggestion negates the entire prompt BOX. If that's the response, then the devs might do better to simply take away the box and have the prompts by themselves, thereby taking away the option to put the content in an unsearchable box.