docs: def ingest(cls, resource, element=None, xpath="ti:citation"):
          """ Ingest xml to create a citation
  
          :param resource: XML on which to do xpath
          :param element: Element where the citation should be stored
          :param xpath: XPath to use to retrieve citation
  
          :return: XmlCtsCitation
          """
          # Reuse of of find citation
          results = resource.xpath(xpath, namespaces=XPATH_NAMESPACES)
          if len(results) > 0:
              citation = cls(
                  name=results[0].get("label"),
                  xpath=results[0].get("xpath"),
                  scope=results[0].get("scope")
              )
  
              if isinstance(element, cls):
                  element.child = citation
                  cls.ingest(
                      resource=results[0],
                      element=element.child
                  )
              else:
                  element = citation
                  cls.ingest(
                      resource=results[0],
                      element=element
                  )
  
              return citation
  
          return None