code: func isISBN10(fl FieldLevel) bool {
  
  	s := strings.Replace(strings.Replace(fl.Field().String(), "-", "", 3), " ", "", 3)
  
  	if !iSBN10Regex.MatchString(s) {
  		return false
  	}
  
  	var checksum int32
  	var i int32
  
  	for i = 0; i < 9; i++ {
  		checksum += (i + 1) * int32(s[i]-'0')
  	}
  
  	if s[9] == 'X' {
  		checksum += 10 * 10
  	} else {
  		checksum += 10 * int32(s[9]-'0')
  	}
  
  	return checksum%11 == 0
  }
docs: // IsISBN10 is the validation function for validating if the field's value is a valid v10 ISBN.