edit mode lock unselected

In edit mode you often need to limit an operation to just a few of the vertices. Currently (as far as I'm aware), the only way to do this is to hide the vertices you dont want affected, by pressing shift + h.

This isn't ideal, because generally you need to see the rest of the model even if you don't want to affect it. Otherwise you're working blind.

I think a lock un-selected option would resolve this problem ...or alternatively ctrl + shift + h to ghost instead of hiding the unselected geometry