The `-link` and `link-offline` options are used to provide a URL and crude list of a contents for external libraries referred to by an API, The list of contents is a file named `package-list` or the newer `element-list` that just lists the _packages_ available in the API. It does not go down to the granularity of even top-level classes and interfaces, let alone members.

Currently, if you want to specify the detailed contents of a library it must be supplied on some suitable source or class path.

It would be better have an option that allows a user to specify the URL for the documentation of a remote library, together with the contents of the library, specified as either source files or class files. The source or class files could be automatically appended to the main source or class path as appropriate.

(Question, what about modular vs non-modular code).

Failing any new option, we should better document (in the man page?) best practices for linking to remote libraries, maybe calling out linking to JDK in particular.