SimpleBindings bindings = new SimpleBindings();
bindings.add(new SortField("_score", SortField.Type.SCORE)); // the score of the document
bindings.add(new SortField("popularity", SortField.Type.LONG)); // the value of the 'popularity' field
FacetSearchParams fsp = new FacetSearchParams(
new SumValueSourceFacetRequest(new CategoryPath("A"), 10, expr.getValueSource(bindings), true));
// Aggregates the facet values
FacetsCollector fc = FacetsCollector.create(fsp, searcher.getIndexReader(), taxoReader);
// MatchAllDocsQuery is for "browsing" (counts facets