Blacklist files and folders

I would like to suggest the ability to blacklist files and folders manually from synchronization.
For example, I want to sync everything in the Documents folder except for the folder ViberDownloads.
ViberDownloads is an application data folder that I cannot move, because Viber insists that it should be in Documents. On my computer this folder takes nearly 3 GB of space and causes sync errors in OwnCloud. I want to omit it from synchronization. But I want to sync the rest of my Documents.

Right now the way to do it is to make the folder “Hidden” which works for this particular folder because I don’t use it. But it won’t work for folders I actually use.

So, please add the ability to manually blacklist folders and individual files from syncing. It would be useful.

This already exists. It is controlled in the ownCloud client using the Selective Sync to exclude folders from synchronization.