Which options are global?

Under the config_dir setting, there's a note that "All global options, such as spool_size, are ignored."

Individual options don't list whether or not they're global - is there a list somewhere that I've missed?

Judging by the preceding sentence,

Each config file must also specify the full Filebeat config hierarchy even though only the prospector part of the file is processed.

I'd assume it means that only prospector configurations are honored, i.e. only nodes under filebeat.prospectors.

That makes sense, but not everything is clearly marked as to whether or not it goes under filebeat.prospectors or just under filebeat.

The examples make some options obvious, but others like publish_async aren't clear since they're nested within options that are global, but don't include an example. Making an educated guess isn't too difficult with most, but making it clear would certainly be helpful.

You can look at the commented out sections of the filebeat.yml file to figure out where to specify options. However, I agree that we could do a better job of describing where to specify options, so I have created an issue in GitHub to track the doc change. https://github.com/elastic/beats/issues/870