General method for discovering the answers to "which header should I include" questions in boost official documentation?

Question

This is an example of countless documentation pages in the Boost.org official docs that completely fail to answer the Question Number Zero: "which header file should I include in order to be able to use this thing"?

What is the secret art of discovering answers to these questions from official boost docs, as opposed to just grepping the sources for definitions?

Answer 1

Note, I'd previously written a fully general response to the question title

To answer the specific example:

Go by the library home page: https://www.boost.org/doc/libs/1_78_0/libs/iterator/doc/ (you can find it from https://www.boost.org/doc/libs/1_78_0/ in case you have trouble guessing the URL).

It will show you a top-level index, and the Specialized Adaptors section mentions function_output_iterator:

Clicking on that link takes you here: https://www.boost.org/doc/libs/1_78_0/libs/iterator/doc/function_output_iterator.html

A fragment from the top of that page: