One or two years ago I was using a selection modifyer (it was a dialogue of some sort) that allowed me to preview live what exactly would be selected. Everything around it was blacked or whited out, I don't remember anymore.

Note: It's not the selection editor, it didn't just show me a white silhouette, it showed me the actual picture I was manipulating.

I know that it had a Feathering option, one for extended or decreasing the radius of the selection to make it a bit smaller or bigger, and probably something else which I'm forgetting.

It was not quick mask mode.

I'm not sure in which GIMP version this was. I only have installers of 2.6.9, 2.6.11, 2.8.0 and 2.8.16, so it could have been in either of these.

I have already searched via Google and couldn't find anything else than the default Feather dialogue when including the word feather, and the gimp help manual for the newest version doesn't yield anything either.

I know that I used this dialogue quite a lot however, and just can't seem to find it anymore for the life of me ... in any of the version I listed.

I hope somebody can help me find this again ... it's really quite annoying to forget something like this.