Highlighting on background layer doesn't show with beamer #19
Description
More specifically, because the highlighting occurs under the page, and the page includes the canvas, if the canvas colour is solid then the highlighting is covered up. The solution will be to hook into an appropriate beamer template instead of the shipout. I just need to figure out which template to hook into, and put in a test for when we're using beamer. Should also add overlay awareness in that case.