code: function obsFws() {
          return opts.strict ? null : wrap('obs-FWS', star(
              and(invis(opt(crlf)), wsp),
              1
          )());
      }
docs: NOTE: read the errata http://www.rfc-editor.org/errata_search.php?rfc=5322&eid=1908 obs-FWS         =   1*([CRLF] WSP)