Number fields in GF are HTML5 <input type="number"> elements. However, it does not take full benefit of HTML5: the min and max values are not set.
In other words, if I make a number field in GF and set the minimum value to 1 and the maximum value to 100, GF should create the element as such: <input type="number" min=1 max=100> which means HTML5-enabled browsers don't allow you to input numbers lower than 1 or higher than 100. Right now, GF does not do this (instead it outputs a text below the input explaining this), so please add this.
For your convenience :) I think this should be added to common.php around line 3000