As I understand, tl;dr stands for too long didn't read. However I came across this post, in which the op said tl;dr at the beginning. What does that mean? Exactly what did the op not read?
"tl;dr" did originally mean "too long, didn't read". But some use it preemptively as if to say "I know this that I wrote is too long, and most won't read it, here is a short version".
Personally I think the best way to use "tl;dr" is not to use it at all. It is disrespectful and dismissive. But many do not agree with that view.