code: func NewSource(opts ...source.Option) source.Source {
  	return &flagsrc{opts: source.NewOptions(opts...)}
  }
docs: // NewSource returns a config source for integrating parsed flags.
  // Hyphens are delimiters for nesting, and all keys are lowercased.
  //
  // Example:
  //      dbhost := flag.String("database-host", "localhost", "the db host name")
  //
  //      {
  //          "database": {
  //              "host": "localhost"
  //          }
  //      }