code: public function setDDI( $ddi )
      {
          $ddi = preg_replace( '/^0+|\D/', '', $ddi );
  
          if (strlen( $ddi ) < 1 || strlen( $ddi ) > 3) {
              throw new InvalidArgumentException( sprintf( 'Invalid DDI (%s)', $ddi ) );
          }
  
          $this->ddi = $ddi;
  
          return $this;
      }
docs: @param  string $ddi
  
  @return $this