private void visit(SimpleIndexedItem item) {
            String indexName = item.getIndexName();
            Index index = getIndexFromUnionOfDocumentTypes(indexName);
            if (index.isPredicate()) {
                errorMessages.add(
                        ErrorMessage.createIllegalQuery(String.format("Index '%s' is predicate attribute and can only be used in conjunction with a predicate query operator.", indexName)));
            }
        }
Checks that predicate queries don't use values outside the defined upper/lower bounds.

@author Magnar Nedland
container-search/src/main/java/com/yahoo/prelude/searcher/ValidatePredicateSearcher.java