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I try to use "summary" when I can as well.

I think few people know the full history of tl;dr. When it first started appearing, it wasn't used by the author, but in response to the author (like you wrote something way too long winded I'm not reading that)

[gist]

Agree most probably don't know the history. TL;DR is a good example of how people can date themselves by how they communicate. They enter into something new and start to copy something that they see because they don't understand the nuance. Then the nuance disappears because of that new usage.

In reverse (with much older people) we have a few customers who pay by check and send a cover letter as well attached to the check (a formal holdover from olden times). Attaching the invoice is sufficient obviously.