docs: def add_footerReference(self, type_, rId):
          """Return newly added CT_HdrFtrRef element of *type_* with *rId*.
  
          The element tag is `w:footerReference`.
          """
          footerReference = self._add_footerReference()
          footerReference.type_ = type_
          footerReference.rId = rId
          return footerReference