code: func IsEmail(s string) bool {
  	if !strings.Contains(s, "@") || string(s[0]) == "@" || string(s[len(s)-1]) == "@" {
  		return false
  	}
  	return true
  }
docs: // IsEmail is a constraint to do a simple validation for email addresses, it only check if the string contains "@"
  // and that it is not in the first or last character of the string
  // https://en.wikipedia.org/wiki/Email_address#Valid_email_addresses