code: protected function generateCheckbox($arrOption, $i)
  	{
  		return sprintf('<input type="checkbox" name="%s" id="opt_%s" class="tl_checkbox" value="%s"%s%s onfocus="Backend.getScrollOffset()"> <label for="opt_%s">%s%s%s</label>',
  						$this->strName . ($this->multiple ? '[]' : ''),
  						$this->strId.'_'.$i,
  						($this->multiple ? StringUtil::specialchars($arrOption['value']) : 1),
  						$this->isChecked($arrOption),
  						$this->getAttributes(),
  						$this->strId.'_'.$i,
  						($this->mandatory && !$this->multiple ? '<span class="invisible">'.$GLOBALS['TL_LANG']['MSC']['mandatory'].' </span>' : ''),
  						$arrOption['label'],
  						($this->mandatory && !$this->multiple ? '<span class="mandatory">*</span>' : ''));
  	}
docs: Generate a checkbox and return it as string
  
  @param array   $arrOption
  @param integer $i
  
  @return string