The yii2-field-range extension enables you to easily setup ActiveField range fields with Bootstrap styling. You basically can setup two attributes joined together like a single field with combined validation error block.
You would find having such a need in most Yii Projects. Your database needs a specific format to store date fields, while you may want to display it in different formats to the users on forms and other views.
Following on from international dates, I also wanted times in the local timezone and format. This was a little more tricky but I think I've got a solution. This is only really appropriate if you have an international app.