A question board lets the author accept one reply as the answer. That is the mechanic I would like to extend by one step: let the author also pin one reply at the top of the thread, with a note about what it is.
Why a separate pin, and not just the accepted answer. The accepted answer is a mechanic for a question: it says "this reply fixed it". A pin is a different thing: it says "read this one first". Some of the best replies on this board are not answers at all — they are a long explanation, a correction of a common mistake, or a piece of context that the thread should not lose.
What I mean in practice. The author picks one reply, and it appears directly under the opening post, above the other replies, labelled with whatever note the author writes. Not moved out of the thread — still in place, still in order, still a reply — just also shown at the top.
Where it would be useful. The threads here that explain something properly are the ones worth reading, and right now the second-best reply in a twenty-reply thread is effectively invisible to anybody who does not scroll. We had a thread about licence files on the Open Source board that would have benefited from exactly this.
What I am not asking for. Not a general pinning system like a forum admin has, where anybody can pin anything. One pin, by the topic author, on their own topic. The same scope as the accepted answer, and it is the same code.