code: function isRegisteredTask(arg) {  
    const flag = this.server ? conf.live_server_packages.includes(arg) : conf.packages.includes(arg);
    if (!flag) {
      console.log('WARNING: a package name (' + arg +') was provided which is not specified in scripts/conf.json. Ignoring it.')
    }
    return flag;
  }
docs: server argument to check against all packages or only those for which starting live-server makes sense