init_refmodel example with custom model

Hi
An older version of projpred had a nice example showing how to use init_refmodel with a custom model:
https://mc-stan.org/projpred/reference/init_refmodel.html

This example no longer work and there is no alternative example on the documentation of init_refmodel. In fact, the current documentation of init_refmodel seems incomplete. For instance, it says

object: Object on which the reference model is created. See possible
types below.

but no types are defined anywhere else.

Would love you see a working example how would you use init_refmodel with your own custom model where you can generate the required samples.

thanks
FKG

Start with the current init_refmodel reference documentation and compare it with the older example linked in the issue. Document the supported object types and add a working example using a custom model that generates the required samples; done when the example works and the documentation is complete.