code: func (v *RegexMatch) IsValid(errors *validate.Errors) {
  	r := regexp.MustCompile(v.Expr)
  	if r.Match([]byte(v.Field)) {
  		return
  	}
  
  	if len(v.Message) > 0 {
  		errors.Add(GenerateKey(v.Name), v.Message)
  		return
  	}
  
  	errors.Add(GenerateKey(v.Name), fmt.Sprintf("%s does not match the expected format.", v.Name))
  }
docs: // IsValid performs the validation based on the regexp match.