code: public static function SUBSTITUTE($text = '', $fromText = '', $toText = '', $instance = 0)
      {
          $text = Functions::flattenSingleValue($text);
          $fromText = Functions::flattenSingleValue($fromText);
          $toText = Functions::flattenSingleValue($toText);
          $instance = floor(Functions::flattenSingleValue($instance));
  
          if ($instance == 0) {
              return str_replace($fromText, $toText, $text);
          }
  
          $pos = -1;
          while ($instance > 0) {
              $pos = mb_strpos($text, $fromText, $pos + 1, 'UTF-8');
              if ($pos === false) {
                  break;
              }
              --$instance;
          }
  
          if ($pos !== false) {
              return self::REPLACE($text, ++$pos, mb_strlen($fromText, 'UTF-8'), $toText);
          }
  
          return $text;
      }
docs: SUBSTITUTE.
  
  @param string $text Value
  @param string $fromText From Value
  @param string $toText To Value
  @param int $instance Instance Number
  
  @return string