A HyperBook is a set of interlinked pages, where each page has a unique ID. The HyperBook as a whole as unique ID as well. The page and HyperDoc IDs are used to specify links.
A HyperDoc is a HyperBook in which the page IDs are the page titles. There is of course a lot more to say about HyperDocs, which is why there are many more pages in the HyperDoc documentation.
A good example for a HyperBook that is not a HyperDoc is . Wikipedia pages have a unique ID, which is the page title. That's all it takes to be a HyperBook. A small amount of code integrates Wikipedia into the HyperBook network, allowing links from HyperDocs to Wikipedia (and, hypothetically, back) that readers can follow while staying in the HyperBook browser.
It should be straightforward to write similar interface code for other Wiki-like HyperBooks, both public ones (on the Web, such as Wikis in Codeberg repositories) and local ones on your computer (your personal , for example).