GIMP :: Showing Masks As Overlay And Command To See Layer Underneath Current One?

1. Is there a "show quick mask" feature for showing masks?

I know Gimp has a "*Show quick mask*" feature which shows what you have(and haven't) selected by displaying a red overlay over your image,allowing you to add to or subtract from a selection by using the paintbrush, but I haven't found a similar feature for showing masks.

Photoshop has this feature (it's called 'reveal mask' I think) and it basically just shows a red overlay of your mask on your image so that,similar to the quick mask feature in Gimp, you can see where you have and haven't masked through.

(I don't own Photoshop so I'm not sure if the red overlay shows the opacity with which you've masked through or whether or not you can edit the mask when it's being shown as a red overlay.)

2. Is there a command for showing the layer underneath the current layer I'm working on?

This is another feature that I've seen Photoshop has that is useful for blending multiple exposures (and lots of things, really).

Basically it's just a keyboard shortcut for showing the layer underneath your current when you hold down a certain keyboard command (it's not something you toggle since it's meant for quickly viewing what's on the layer underneath your current one).

I know I can press space bar to show or hide the layer I'm currently working on, but I can't do that unless I focus into the layers dialogue first. It'd be nice if I could activate that functionality from anywhere,regardless of whether I'm focused on the layers dialogue.

Do either of these features exist in Gimp?