public String getArgumentString() {
        if (sourceString != null) return sourceString;

        List<Item> items = new ArrayList<>(items());
        if (hasStartAnchor())
            items.remove(0);
        if (hasEndAnchor())
            items.remove(items.size() - 1);
        return items.stream().map(item -> ((WordItem)item).getWord()).collect(Collectors.joining(" "));
    }
Returns the canonical form of the tokens of this: Either the source string, or if none
each token except the start and end anchor separated by space
container-search/src/main/java/com/yahoo/prelude/query/UriItem.java