public void setStrength(Strength value) {
        verifyThat(sortStrength == null, "sorting already has strength", sortStrength);
        this.sortStrength = value;
    }
This class holds the extracted information after parsing a "sorting"
block, using simple data structures as far as possible.  Do not put
advanced logic here!
@author arnej27959
config-model/src/main/java/com/yahoo/schema/parser/ParsedSorting.java