code: def citedby_pid(self, pid, metaonly=False, from_heap=True):
          
  
          if from_heap is True:
              result = citations.raw_data(pid)
  
              if result and 'cited_by' in result and metaonly is True:
                  del(result['cited_by'])
                  return result
  
              if result:
                  return result
  
          url = urljoin(self.CITEDBY_URL, self.PID_ENDPOINT)
  
          params = {
              "q": pid,
              "metaonly": "true" if metaonly is True else "false"
          }
  
          result = self._do_request(url, params=params)
  
          return result
docs: Retrieve citedby documents from a given PID number.
  
          pid: SciELO PID number
          metaonly: will retrieve only the metadata of the requested article citations including the number of citations it has received.
          from_heap: will retrieve the number of citations from a preproduced report, it will not fetch the api. Much faster results but not extremely updated.