About the interface keyword

The interface keyword defines an interface. An interface is similar to a class, with the following important differences:

Interfaces contain only declarations of methods, not their implementation. That is, every class that implements an interface must provide an implementation for each method declared in the interface.
Only public members are allowed in an interface definition; static and class members are not permitted.
The get and set statements are not allowed in interface definitions.
To use the interface keyword, you must specify ActionScript 2.0 and Flash Player 6 or later in the Flash tab of your FLA file's Publish Settings dialog box.

The interface keyword is supported only when used in external script files, not in scripts that you write in the Actions panel.