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I'd be inclined to put a summary at the beginning, similar to an abstract in an academic paper. That way people would see it first, those who were interested could read further, and those who were ...
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#3: Attribution notice added
Source: https://writers.stackexchange.com/a/32828 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#2: Initial revision
I'd be inclined to put a summary at the beginning, similar to an abstract in an academic paper. That way people would see it first, those who were interested could read further, and those who were not would still see the summary. Putting it at the end might lead those who weren't particularly interested to feel they had wasted time getting there, and those who were to think "what do you mean? That was just fine." You've already identified "tl;dr" as slang, so all the usual questions about where slang works and where it doesn't will apply. This particular one isn't one of my favourites - if the writer really thinks the post is too long, why didn't they do something about it? The other thing about slang is it can date quite quickly. It might look groovy now, but in a year or so the posts might look like they were written by a square.