Random 'concerns' folders and '.keep' files

I am learning rails.

Somewhere along the line, I noticed that seemingly random folders and files are appearing in my rails app’s directory. In some folders there is a concerns folder with a .keep file inside it. The .keep file appears to be empty. In other folders there is no concerns folder but an empty .keep file is present.

Does anyone know what the deal with these files/folders is?

.keep files are especially helpful when you want to commit empty directories with git.

The .keep files are there to prevent portage from one vcs to another, deleting important directories when you unmerge something that would cause those directories to be empty. It’s a software design paradigm which seeks to decrease the number of decisions that developers need to make, gaining simplicity, but not necessarily losing flexibility.