List<String> getReferencedDocuments() {
        var result = new ArrayList<String>();
        for (var field : docFields.values()) {
            var type = field.getType();
            if (type.getVariant() == ParsedType.Variant.DOC_REFERENCE) {
                var docType = type.getReferencedDocumentType();
                assert(docType.getVariant() == ParsedType.Variant.DOCUMENT);
                result.add(docType.name());
            }
        }
        return result;
    }
This class holds the extracted information after parsing a
"document" block in a schema (.sd) file, 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/ParsedDocument.java