Currently results returned by list_* functions can be "raw" XML, XML past to a "list" or to "df". It could rather easily return additionally:

• as="xml" - parsed XML as a xml_document object (in while_oai use xml_orig)
• as="xml_list" - a verb-related subtree of XML, e.g. for list_records the tag <ListRecords> (in while_oai use xml object).

XML is already parsed so we get those for free. It is useful to use them in dumper functions - no need to parse raw XML again.