This project is basically translated php project from Georgi Chorbadzhiyski, for the original project click here You can find the information, about how the validation is processed in Wikipedia as well

• As method -> bool isValid = Egn.isValid({the Personal id you want to validate in string});
• As ValidationAttribute ->
  [EGN]
  public string personalId { get; set; }
  or
  [EGN(ErrorMessage="Your error message")]
  public string personalId { get; set; }