Boosting on different fields #2340

How can I define boosts for query terms but also specify the field? For example, I have title, entities and contents and I want to specify different boosts on each of them.
I don't find it in the documentation:
https://github.com/castorini/pyserini/blob/master/docs/usage-querybuilder.md
https://github.com/castorini/pyserini/blob/master/pyserini/search/lucene/querybuilder.py