Hello everyone,
It can be benefited from the type number in HTML5 by replacing type="text" for type="number" for the addtocart quantity:
line 90 in /sublayouts/addtocartbar.php
replace
$editable = 'text';
for
$editable = 'number';
Although for the productdetails pages and category views it is a duplication of the already present + and - buttons, it is useful in the checkout view, as the quantities of the products in the cart can be easily changed (by two clicks).