The difference between bulkrenameutility isset and empty

isset($var); //It is false, it is not defined, it is not defined as false
$var = '';
isset($var); //It is true, it is defined as true
empty($var); //It is true value If it is empty, return true
$var = '111';
empty($var); //If it is false, if it is not empty, return false

The above introduces the difference between bulkrenameutility isset and empty, including the content of bulkrenameutility. I hope it will be helpful to friends who are interested in PHP tutorials.