Generators should generate tagfiles in the doxygen format. Tagfiles contain a list of symbols and their relative urls. They allow for documentation to refer to symbols in other documentation.

Here are some examples:

https://github.com/alandefreitas/url/blob/update-antora/doc/lib/cpp_tagfiles/cppreference-doxygen-web.tag.xml
https://github.com/alandefreitas/url/tree/update-antora/doc/tagfiles

We already have an Antora extension for the Antora documentation to use these tagfiles. I copied some logic from the collector extension to allow components to set their tagfiles besides tagfiles that might be set in the playbook.