public void addNestedField(ImportedField importedField) {
        String prefix = fieldName() + ".";
        assert(importedField.fieldName().substring(0, prefix.length()).equals(prefix));
        String suffix = importedField.fieldName().substring(prefix.length());
        nestedFields.put(suffix, importedField);
    }
A complex field that is imported from a concrete field in a referenced document type and given an alias name.
config-model/src/main/java/com/yahoo/schema/document/ImportedComplexField.java