Under what conditions does "select non-manifold not show up in the select menu? I use blender to create designs for 3d printing.   I use select non-manifold a lot to look for problems as I work on a design.   I see that sometimes select non-manifld doesn't show up in the select menu.

I don't know if it's just for the more complicated designs or not, so I'm wondering if anyone knows under what conditions select non-manifold is not available.
You must be in vertex-edit mode in order to have that option.

Edit: orrrr edge-edit mode, confirmed.