Thank you, but Jesus H Christ. Why is the default zero? The Blender developers really have a disdain for new users, don’t they? I mean, they really, really don’t care.
EDIT: It’s also impressive how they repeatedly screw you over if you don’t happen to know the exact correct file format for again which there are no hints at all in the UI…
EDIT 2: Ok, so this is apparently (I think?) how a “correct” glare setup should look like. But I had to figure out and “design” this UI myself (and I still don’t have a “save as” button, I need to re-render when I want a new file). It’s absolutely a travesty that new users have to go through this for something so simple.