Thanks to the help of some other users I keep on the develop of this little web aplication.
In fact is a kind of calculator. So, this step leads to reach a very special behaviour of a textBox. This time, it must act as an input of a range of numbers from 0 to 3. Only numbers!
So, I've developed this project (Here you can find the project capx)
Here you can find an image:
Do you know what to modify to make it act the way I want?