code: function domainLiteral() {
          return wrap('domain-literal', and(
              invis(opt(cfws)),
              literal('['),
              star(and(opt(fws), dtext)),
              opt(fws),
              literal(']'),
              invis(opt(cfws))
          )());
      }
docs: domain-literal  =   [CFWS] "[" *([FWS] dtext) [FWS] "]" [CFWS]