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