What is the significance of the isset() and !empty() functions in the suggested solution for changing the $_width_max_ variable?

The isset() function is used to check if a variable is set and not null, while the !empty() function is used to check if a variable is not empty. In the suggested solution for changing the $_width_max_ variable, these functions are used to ensure that the variable is set and has a value before updating it with a new value.

if(isset($_POST['width_max']) && !empty($_POST['width_max'])){
    $_width_max_ = $_POST['width_max'];
}