@Override
    public Sorting clone() {
        try {
            return (Sorting)super.clone();
        }
        catch (CloneNotSupportedException e) {
            throw new RuntimeException("Programming error");
        }
    }
A search-time document attribute sort specification(per-document in-memory value).
This belongs to the attribute or field(implicitt attribute).

@author baldersheim
config-model/src/main/java/com/yahoo/schema/document/Sorting.java