code: def _validate_rfilter(self, rfilter, letter="d"):
          
          if letter == "d":
              pexdoc.exh.addai(
                  "dfilter",
                  (
                      (not self._has_header)
                      and any([not isinstance(item, int) for item in rfilter.keys()])
                  ),
              )
          else:
              pexdoc.exh.addai(
                  "rfilter",
                  (
                      (not self._has_header)
                      and any([not isinstance(item, int) for item in rfilter.keys()])
                  ),
              )
          for key in rfilter:
              self._in_header(key)
              rfilter[key] = (
                  [rfilter[key]] if isinstance(rfilter[key], str) else rfilter[key]
              )
docs: Validate that all columns in filter are in header.