Code considerations capture our experiences working on the standard library for all contributors. If you come across something new or unexpected then a code consideration is a great place to record it. Then other contributors and reviewers can find it by searching the guide.
Code considerations are a bit like guidelines. They should try make concrete recommendations that reviewers and contributors can refer to in discussions. A link to a real case where this was discussed or tripped us up is good to include.
Code considerations should also try include a For reviewers section. These can call out specific things to look out for in reviews that could suggest the consideration applies. They can also include advice on how to apply it.
It's more important that we capture these experiences somehow though, so don't be afraid to drop some sketchy notes in and debate the details later!