code: protected function getInstance($selector = '')
      {
          if (empty($this->object)) {
              throw new \RuntimeException('Editor instance was not set.');
          }
  
          if (empty($this->selector) && empty($selector)) {
              throw new \RuntimeException('No such editor was not selected.');
          }
  
          $this->setSelector($selector);
  
          if (empty($this->instances[$this->selector])) {
              $instanceId = $this->context->element('field', $this->selector)->getAttribute('id');
              $instance = sprintf($this->object, $instanceId);
  
              if (!$this->context->executeJs("return !!$instance")) {
                  throw new \Exception(sprintf('Editor "%s" was not found.', $instanceId));
              }
  
              $this->instances[$this->selector] = $instance;
          }
  
          return $this->instances[$this->selector];
      }
docs: Get the editor instance for use in Javascript.
  
  @param string $selector
  Any selector of a form field.
  
  @throws \RuntimeException
  @throws \Exception
  @throws \WebDriver\Exception\NoSuchElement
  
  @return string
  A Javascript expression that representing WYSIWYG instance.