rank_feature field can index numbers so that they can later be used to boost
documents in queries with a
Rank feature fields must use the
Rank features that correlate negatively with the score need to declare it
rank_feature fields only support single-valued fields and strictly positive
values. Multi-valued fields and negative values will be rejected.
rank_feature fields do not support querying, sorting or aggregating. They may
only be used within
rank_feature fields only preserve 9 significant bits for the precision, which
translates to a relative error of about 0.4%.
Rank features that correlate negatively with the score should set
false (defaults to
true). This will be used by
rank_feature query to modify the scoring formula
in such a way that the score decreases with the value of the feature instead of
increasing. For instance in web search, the url length is a commonly used
feature which correlates negatively with scores.