restrict input

I need to restrict the front end field input to only 10 characters but i put ten into the back end feild to restrict it and nothing happens.

I have tried to use the link provided below the ‘input restrictions’ section and i have played around with the code on the page by putting it into the field on the back end to try restrict the input on the front end to only 10 characters but it doesnt restrict the user from inputting more than 10 characters into the field.