src/MimeMailer/MimeMessage.php
public function setHtml($html = '', $clear = false)
    {
        if (true===$clear) {
            $this->clear('text');
        }
        $this->html .= Helper::formatText($html, 'ascii');
        return $this;
    }
public function setHtml($html = '', $clear = false)
    {
        if (true===$clear) {
            $this->clear('text');
        }
        $this->html .= Helper::formatText($html, 'ascii');
        return $this;
    }
Set HTML version

@param string $html The HTML content
@param bool $clear Clear a set content first ? (default is to append a content)
@return self