This method does not modify the existing
$page object but returns a new object with the changes applied. Learn more →
Kirby's objects are immutable. That means, when you modify an object like
$file etc. using a method like
changeTitle() and so on, a new object is returned. Therefore, you have to store the returned object in a new variable to be able to further work with it.
The increment method will only work reliably with field values that PHP can parse into a valid integer. Otherwise the field value will be evaluated as zero and incremented to 1 or whatever $by value you pass.