private void assertEqualElementsSelector(SummaryField field1, SummaryField field2) {
        if ( ! field2.getElementsSelector().equals(field1.getElementsSelector())) {
            throw new IllegalArgumentException("Conflicting summary elements selectors. " + field2.toLocateString() +
                    " is already defined as " +
                    field1.toLocateString() + ". A field with the same name " +
                    "can not have different element selectors in different summary classes");
        }
    }
Ensure that summary field transforms for fields having the same name
are consistent across summary classes

@author bratseth
config-model/src/main/java/com/yahoo/schema/processing/SummaryConsistency.java