In the notification page, you will create the basic look of your notification. You can have it fit in with your gtk theme by checking the 'Use Gtk theme background' or you can choose to use an image. Guifications supports 1-bit alpha which you can use to create non-rectangular notifications.
If you choose to use the Gtk theme's background, you can decide how big you want the notification. If you decide that you want to use an image as the background, the notification size will be set to the size of the image. If the image is non-rectangular, it will still use the resolution of the image.
The alias entry has been added for those of you that would like to support multiple notifications of the same type in a theme. By using aliases, you can tell at a glance which notification is which. Hopefully this will prove to be useful for someone besides me. :)