This is my first post here, sorry if I violate any community norms! 
We are developing lessons for version-control beginners, using git and RStudio IDE. We simulate a merge conflict and have the students resolve it. I noticed that a "U" appears next to the conflicted file in the git tab. However, I could not find any documentation for what it stands for. The "RStudio IDE Cheat Sheet" only lists what the A, D, M, R, and ? stand for. Is there a full list of these abbreviations? It might also be helpful to add "U" to future versions of the cheatsheet.
Edit: Here is another place where the "U" is mentioned but not explained what it stands for: http://r-pkgs.had.co.nz/git.html#git-pull ... I'm just gonna guess "unresolved!"