As far as I can tell this topic has not been discussed, but I could be wrong.
I would expect, when searching in a parent folder, that the search results would also return papers in child folders as well.
Clearly it is convenient to use both tags and folders to organize papers (proven by the existence by both in this and many other similar software tools). Given that a child folder is automatically related to a parent folder it seems like the results of a search in a parent folder should also include those of the same search in the child folders.
1. Some may not want this behavior for some reason (i'm not sure why, but that is why I am bringing this up and they aren't) -- but this could easily be fixed by some kind of setting (`return matches from child folders' or something like that)
2. Maybe the results could be clearly marked as from a child folder it that is important to someone.
In my opinion when I search I want more results not less. I want to focus on the main folder for the project I am working on and be able to search all papers within it. I don't want to have to remember which child folder (or possibly grand-child folder) the paper might be contained in.
Currently to bypass the limitation I perform searches in the `All Papers' view, but that can sometimes get very messy due to the overall size of my library.