src/ExternalURLField.php
public function getAttributes()
    {
        $attributes = array(
            'placeholder' => $this->config['defaultparts']['scheme'] . "://example.com" //example url
        );
        if ($this->config['html5validation']) {
            $attributes += array(
                'type' => 'url', //html5 field type
                'pattern' => 'https?://.+', //valid urls only
            );
        }

        return array_merge(
            parent::getAttributes(),
            $attributes
        );
    }
public function getAttributes()
    {
        $attributes = array(
            'placeholder' => $this->config['defaultparts']['scheme'] . "://example.com" //example url
        );
        if ($this->config['html5validation']) {
            $attributes += array(
                'type' => 'url', //html5 field type
                'pattern' => 'https?://.+', //valid urls only
            );
        }

        return array_merge(
            parent::getAttributes(),
            $attributes
        );
    }
Set additional attributes
@return array Attributes