How to get custom API documentation page?

The API Catalogue docs state that it is possible to use a custom CMS page for the api documentation. However I see no way to actually make that association in the dashboard UI. You can only attach swagger or blueprint definitions. Looking at the catalogue template, it also seems to only use the generated IDs with specific api documentation URLs that would not support a custom CMS page.
Is this really possible, and if so how?
We have custom HTML documentation that we want to show with the API.

You can’t directly link it to an API entry yet, though you can use the page + menu functionality to construct a markdown-based page structure that documents your API.

You could use the fact that the description of the API entry supports markdown to link to your custom docs instead of having the large button.

If you are self hosted, you can set up your own templates with content fields and target them from the page editor so that you can give your docs a specific style.