Masking in Edit Mode

Sometimes you need to move vertices using Proportional Editing, but without affecting certain vertices, so maybe there should be a Masking feature to freeze those vertices (just like in Sculpt Mode, and the vertices masked out should be darker). I know what you're thinking "you can hide the vertices you don't want to be moved", but what if you want to see them, even if you don't want to move them, just for reference?

I think a Masking tool in Edit Mode is a great idea because it's not even something new, Sculpt mode has it, and with that in mind you should be able to mask out certain vertices in Edit mode, then switch to Sculpt mode, while keeping those same vertices masked out (and the other way round). It should work the same as in Sculpt mode, I mean with a Weight that tells how much masked the vertices are (so is perfectly compatible with the Masking of Sculpt mode).