Aseprite V 1.3.6
This is a very minor UX issue.
When the onion skin frame range is set so that one end of the range is within the current selected frame, it is actually quite difficult to change the range. The margin that the mouse has is extremely thin. In fact, it seems to be impossible to drag the onion skin range to the left when the range starts at the current selected frame. This makes some sense as you generally don’t want to edit the onion skin range all the often, and it is common a user will want to select multiple frames at once.
However, it took me awhile to realize that I could select an individual layer within a frame like below.
I think that grabbing onto the onion skin range selector should be a little easier when a whole frame is selected. Unfortunately, I don’t have a good solution as to how this could be done. And again, it is an extremely minor problem, but I think this is a difficult and specific problem to google if a user is having trouble and the solution is not all that obvious, especially for a new user.