@Override
    public void process(boolean validate, boolean documentsOnly) {
        for (var entry : schema.getSummaries().entrySet()) {
            var summary = entry.getValue();
            for (var field : summary.getSummaryFields().values()) {
                if (field.getElementsSelector().getSelect() == SummaryElementsSelector.Select.BY_MATCH ||
                    field.getElementsSelector().getSelect() == SummaryElementsSelector.Select.BY_SUMMARY_FEATURE) {
                    processSummaryField(summary, field, validate);
                }
            }
        }
    }
Iterates all summary fields with 'matched-elements-only' or 'select-elements-by' and validates that the field type is supported.

@author geirst
config-model/src/main/java/com/yahoo/schema/processing/SummaryElementsSelectorValidator.java