Updated Guide
We've been working on this for a while, we hope that it should make the process of adding Adult Content Warnings easier, and make those content warnings more informative.
If you have any questions it'll be quicker and easier to contact us directly than to comment here, but obviously we're open to feedback on the content warnings, their definitions and their implementation. I don't intend to spend too much time on hypotheticals, I think the content warnings we have cover most adult content, and anything else is either not adult content or can be handled by custom content warnings.