I also want to know where should we locate _output.yml to share the settings among vignettes.
Is it package root or vignettes directory or some where else?
Not sure if _output.yml is widely used in the vignette building scenario. It is possible that the logic of global setting using this file do not apply well due to how vignette works (vignettes/ folder then doc/
What did you try already ? Usually it should be in the root directory of the rmd file, so vignette directory ?
Know that you should be able to set a specific path per document.
output_yaml: <path/to/yaml>
in case it could be useful.
We could definitely adapt rmarkdown to make your scenario works if needed.
There, I discuss which features to be included by default.
However, I understand there is no default that can satisfy all users.
Now I think I should let almost all the features be opt-in.
Then, _output.yml would be a nice shortcut for users to prepare their own defaults.