- This is an option, and by default it has the previous behavior: look only for visible element
- This option allows us to look for non-visible elements
- Using new altInput from flatpickr create a input hidden element. This is why we need to look at this element.
- Using the altInput from flatpickr forces us to use this default date format
- As we now use `altInput` from flatpickr, the value used to communicate between backend and frontend is stored into an input type hidden.