ActionScript 3: Restricting the Characters That Can be Entered in a Text Field

Apparently this ability has existed forever, but since it is incredibly handy I am making a note of it. It is possible to restrict the set of characters that can be typed into a text field in Flash. This Adobe example allows only uppercase characters, spaces, and numbers to be entered into a text field:

my_txt.restrict = "A-Z 0-9";