src/RijksregisternummerHelper.php
/**
   * Returns true if an identification number of the National Register is a bisnummer, false otherwise.
   *
   * @param string $rijksregisternummer The clean and valid identification number of the National Register.
   *
   * @return bool
   *
   * @since 1.0.0
   * @api
   */
Returns true if an identification number of the National Register is a bisnummer, false otherwise.
@param string $rijksregisternummer The clean and valid identification number of the National Register.

@return bool


Returns true if an identification number of the National Register is a bisnummer false otherwise . @param string $rijksregisternummer The clean and valid identification number of the National Register . @return bool
public static function isBis(string $rijksregisternummer): bool
  {
    $month = (int)substr($rijksregisternummer, 2, 2);
    if (21<=$month && $month<=52)
    {
      return true;
    }
    return false;
  }
public static function isBis ( string $ rijksregisternummer ) : bool { $ month = ( int ) substr ( $ rijksregisternummer , 2 , 2 ) ; if ( 21 <= $ month && $ month <= 52 ) { return true ; } return false ; }
Returns true if an identification number of the National Register is a bisnummer, false otherwise.
Returns true if an identification number of the National Register is a bisnummer false otherwise .