code: def _findCRefPattern(self, xml):
          
          if not self.citation.is_set():
              citation = xml.xpath("//tei:refsDecl[@n='CTS']", namespaces=XPATH_NAMESPACES)
              if len(citation):
                  self.citation = Citation.ingest(resource=citation[0], xpath=".//tei:cRefPattern")
              else:
                  raise MissingRefsDecl("No reference declaration (refsDecl) found.")
docs: Find CRefPattern in the text and set object.citation
          :param xml: Xml Resource
          :type xml: lxml.etree._Element
          :return: None