private Item instantiateWordItem(String field,
                                     OperatorNode<ExpressionOperator> ast,
                                     Class<?> parent,
                                     SegmentWhen segmentPolicy) {
        String wordData = getStringContents(ast);
        return instantiateWordItem(field, wordData, ast, parent, segmentPolicy, null, decideParsingLanguage(ast, wordData));
    }
Build a "pure" not, without any positive terms.
container-search/src/main/java/com/yahoo/search/yql/YqlParser.java