code: def _parse_w_comma_h(self, whstr, param):
          
          try:
              (wstr, hstr) = whstr.split(',', 2)
              w = self._parse_non_negative_int(wstr, 'w')
              h = self._parse_non_negative_int(hstr, 'h')
          except ValueError as e:
              raise IIIFRequestError(
                  code=400, parameter=param,
                  text="Illegal %s value (%s)." % (param, str(e)))
          if (w is None and h is None):
              raise IIIFRequestError(
                  code=400, parameter=param,
                  text="Must specify at least one of w,h for %s." % (param))
          return(w, h)
docs: Utility to parse "w,h" "w," or ",h" values.
  
          Returns (w,h) where w,h are either None or ineteger. Will
          throw a ValueError if there is a problem with one or both.