Keep Selection Between Selection Types

Yes, I realize that the title is cryptic but I really don't know what the different "selection types" as a whole are called. Anyway;

I read about this somewhere and I could do it in Max 8 but I forgot the button; what do you hold while changing selection types (ie. vertex, edge, face, polygon, element) to keep your selection? What I mean is you want to select a line in edge but it's hard to do that with out first over selective and then removing the things you don't want from your selection. I know that if i select all the vertices that make up the line I want to select and hold a certain button, shift, ctrl, alt, or something, while changing to edge it then gives me a line made up of those vertices I had selected.

My question is, what is the button? I've tried both shift, ctrl, and alt and none of them work.

EDIT: fuuuu... It's shift in edit poly... still want one for edible mesh if any one knows of one.

EDIT: ok, in edit poly shift keeps an outline, ctrl keeps it all, and alt doesn't do anything