private boolean phraseArgumentSupported(Class<?> parent) {
        if (parent == null) return true;

        // not supported in backend, but the container flattens the arguments itself:
        if (parent == PhraseItem.class) return true;

        return parent == EquivItem.class;
    }
Converts the payload of a contains statement into an Item

@param exactMatch true to always create an ExactStringItem, false to never do so, and null to
                  make the choice based on the field settings
container-search/src/main/java/com/yahoo/search/yql/YqlParser.java