Hello, I am a korean learner, but I am sure this feature could be useful to anybody.

It would be nice to be able to create advanced grouping feature among existing card sets.

For example in my case I have a group "Speaking" and a group "Thoughts". They have however respectively words (for example) "마르다" and "모르다". It would nice then given existing groups creating subgroups that can enable me to group words based in the "르다" suffix.

So I can then train on that group without having issues with duplicated cards.

Hello! I‘ve been using Duocards for three years ago and over the course of time I created a lot of cards from differents sources (different books). I create a folder per unit (one folder for unit 1, and another one for unit 2 and so on) but I think just one level of folders is not enough for me because I have plenty of them, especially because I extracted information and created cards from differents books so I have +100 folders and I find very tedious to filter folders efficiently in the way the app enables currently. It would be great I if could classify the folders (units - First level) into subfolders (for example sections of the books - second level) and what's more, sections according to one particular books (third level). I know I classify cards in a particular way but I am sure that every user with a considerable numbers of cards created is facing a similar difficulty. If You didn‘t create such numbers of folders yet take for sure that you will have this problem sooner or later

It would be nice if it would be possible to merge personal folders, or create sub-folders inside deks. With the time you end up having way too many folders so it becomes annyoing to select/deselect what I need to practice.