code: function obsDomainList() {
          return opts.strict ? null : wrap('obs-domain-list', and(
              star(or(invis(cfws), literal(','))),
              literal('@'),
              domain,
              star(and(
                  literal(','),
                  invis(opt(cfws)),
                  opt(and(literal('@'), domain))
              ))
          )());
      }
docs: obs-domain-list =   *(CFWS / ",") "@" domain *("," [CFWS] ["@" domain])