code: func Boolean(in []byte, pos int) (int, error) {
  	switch in[pos] {
  	case 't':
  		return expect(in, pos, t...)
  	case 'f':
  		return expect(in, pos, f...)
  	default:
  		return 0, errUnexpectedValue
  	}
  }
docs: // Boolean matches a boolean at the specified position