code: public function switchUser($row, $href, $label, $title, $icon)
  	{
  		$blnCanSwitchUser = ($this->User->isAdmin || (!empty($this->User->amg) && \is_array($this->User->amg)));
  
  		if (!$blnCanSwitchUser)
  		{
  			return '';
  		}
  
  		if (!$row['login'] || $row['username'] == '' || (!$this->User->isAdmin && \count(array_intersect(Contao\StringUtil::deserialize($row['groups'], true), $this->User->amg)) < 1))
  		{
  			return Contao\Image::getHtml(preg_replace('/\.svg$/i', '_.svg', $icon)).' ';
  		}
  
  		return '<a href="contao/preview.php?user='.rawurlencode($row['username']).'" title="'.Contao\StringUtil::specialchars($title).'" target="_blank">'.Contao\Image::getHtml($icon, $label).'</a> ';
  	}
docs: Generate a "switch account" button and return it as string
  
  @param array  $row
  @param string $href
  @param string $label
  @param string $title
  @param string $icon
  
  @return string