It's about emails, but I like this article[0] about how topics are covered in the military (where I imagine clear communication is important). "Military professionals lead their emails with a short, staccato statement known as the BLUF (Bottom Line Up Front). It declares the purpose of the email and action required.". I find this helpful..
The BLUF is exactly analogous to what the internet hivemind calls the tl;dr (too long; didn't read). I almost always see the tl;dr as the last line of a long post, when really, it makes a lot more sense to lead with it.
Seconded. I always put TL;DR at the beginning if it's meant as an actual summary. I sometimes put a TL;DR at the end, when it's meant as a humorous summary.
[0] https://hbr.org/2016/11/how-to-write-email-with-military-pre...