public CellMapHelper bind(String label) {
        if (labels.size() >= meta.mappedDims().size()) {
            throw new IllegalArgumentException("At " + address() + ": Got label '" + label +
                                               "' but all mapped dimensions already have labels");
        }
        List<String> next = new ArrayList<>(labels);
        next.add(label);
        return new CellMapHelper(meta, next);
    }
Helper to incrementally build addresses and insert values (expression nodes) into a map.
Only used as an internal component of the RankingExpression parser.
@author arnej
searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/parser/CellMapHelper.java