public boolean doesSummarying() {
        if (usesStruct()) {
            for (SDField structField : getStructFields()) {
                if (structField.doesSummarying()) {
                    return true;
                }
            }
        }
        return containsExpression(SummaryExpression.class);
    }
Returns true if (there is strong evidence that) the value stored by this field is bit-packed.
config-model/src/main/java/com/yahoo/schema/document/SDField.java