For a recent project, I needed to inspect the data incoming comments before any of the other filtering on the data took place. Sounds like a big snore-fest, right? In WordPress, preprocess comment filtering is something that’s actually really easy to do, but the thing is that the documentation was lacking.
Anyway, I did actually find a hook that allowed me to do what I needed to do, though there was no official Codex page explaining exactly how to use the filter.
As such, here’s a break down of exactly what I was trying to do, and then a link to the of the Codex article I drafted after I ended up getting familiar with the hook.