code: public function setNumber( $number )
      {
          $number = preg_replace( '/^0+|\D/', '', $number );
  
          if (strlen( $number ) !== 9 && strlen( $number ) !== 8) {
              throw new InvalidArgumentException( sprintf( 'Invalid Number (%s)', $number ) );
          }
  
          $this->number = $number;
  
          return $this;
      }
docs: @param  string $number
  
  @return $this