Searching by field

Perhaps this is a silly question, but how do I search by field?

For instance, I want to narrow down my searches by host/site, I was trying to do this:
curl http://localhost:8081/json -d"q=about&facet.field=site&facet.query=\"\""

But l get “Invalid facet field: site”


Supported fields are here. (site is not in that as default)
To add site, modify as below:


Thank you!