code: def _check_fact_ref_eval(cls, cpel_dom):
          
  
          CHECK_SYSTEM = "check-system"
          CHECK_LOCATION = "check-location"
          CHECK_ID = "check-id"
  
          checksystemID = cpel_dom.getAttribute(CHECK_SYSTEM)
          if (checksystemID == "http://oval.mitre.org/XMLSchema/ovaldefinitions-5"):
              # Perform an OVAL check.
              # First attribute is the URI of an OVAL definitions file.
              # Second attribute is an OVAL definition ID.
              return CPELanguage2_3._ovalcheck(cpel_dom.getAttribute(CHECK_LOCATION),
                                               cpel_dom.getAttribute(CHECK_ID))
  
          if (checksystemID == "http://scap.nist.gov/schema/ocil/2"):
              # Perform an OCIL check.
              # First attribute is the URI of an OCIL questionnaire file.
              # Second attribute is OCIL questionnaire ID.
              return CPELanguage2_3._ocilcheck(cpel_dom.getAttribute(CHECK_LOCATION),
                                               cpel_dom.getAttribute(CHECK_ID))
  
          # Can add additional check systems here, with each returning a
          # True, False, or Error value
          return False
docs: Returns the result (True, False, Error) of performing the specified
          check, unless the check isnt supported, in which case it returns
          False. Error is a catch-all for all results other than True and
          False.
  
          :param string cpel_dom: XML infoset for the check_fact_ref element.
          :returns: result of performing the specified check
          :rtype: boolean or error