core-bundle/src/Resources/contao/library/Contao/Widget.php
protected function isSelected($arrOption)
	{
		if (empty($this->varValue) && empty($_POST) && $arrOption['default'])
		{
			return static::optionSelected(1, 1);
		}

		return static::optionSelected($arrOption['value'], $this->varValue);
	}
protected function isSelected($arrOption)
	{
		if (empty($this->varValue) && empty($_POST) && $arrOption['default'])
		{
			return static::optionSelected(1, 1);
		}

		return static::optionSelected($arrOption['value'], $this->varValue);
	}
Check whether an option is selected

@param array $arrOption The options array

@return string The "selected" attribute or an empty string