Investigate if it's possible to document HTTP headers more strictly without it becoming too laborious

[wilkinsona]

When support for documenting HTTP headers was added a decision was made that, unlike the other snippets, a failure would not occur if a header wasn't documented. This was to avoid problems with headers that are very commonly sent or received but typically don't warrant documentation such as Content-Length.

This seems to have worked well for making it easy to document HTTP headers, but has come at the cost of headers sometimes going undocumented. It would be nice to adjust the balance a little so that headers aren't missed and, hopefully, so that documenting headers remains an easy thing to do