protected boolean known(HitGroup source, Hit hit, Execution execution) {
            String stripID = getProperty(hit, blendingField);

            if (stripID == null) {
                if (!source.isFilled(result.getQuery().getPresentation().getSummary())) {
                    Result nResult = new Result(result.getQuery());
                    nResult.hits().add(source);
                    fill(nResult, nResult.getQuery().getPresentation().getSummary(), execution);
                    stripID = getProperty(hit, blendingField);
                    if (stripID == null) {
                        return false;
                    }
                } else {
                    return false;
                }
            }

            if (documentsToStrip.contains(stripID)) {
                return true;
            }

            documentsToStrip.add(stripID);
            return false;
        }
Produce a single blended hit list from a group of hitgroups.

This assumes that all hits are organized into hitgroups. If not, blending will not be performed.
container-search/src/main/java/com/yahoo/prelude/searcher/BlendingSearcher.java