code: public function setText($text = '', $clear = false)
      {
          if (true===$clear) {
              $this->clear('text');
          }
          if ('auto'==$text) {
              if (!empty($this->html)) {
                  $html_content = preg_replace("/.*<body[^>]*>|<\/body>.*/si", "", $this->html);
                  $this->text .= Helper::formatText(Helper::html2text($html_content));
              }
          } else {
              $this->text .= Helper::formatText($text);
          }
          return $this;
      }
docs: Set plain text version
  
  If $text='auto', the text version will be generated from the HTML content
  
  @param string $text The plain text content or keyword 'auto' to auto-generate it from the HTML content
  @param bool $clear Clear a set content first ? (default is to append a content)
  @return self