outlines – Produce "outline" lists

De­fines an out­line en­vi­ron­ment, which al­lows out­line-style in­dented lists with freely mixed lev­els up to four lev­els deep. It re­places the nested be­gin/end pairs by dif­fer­ent item tags \1 to \4 for each nest­ing level. This is very con­ve­nient in cases where nested lists are used a lot, such as for to-do lists or pre­sen­ta­tion slides.