MACROMEDIA FLASH 8-ACTIONSCRIPT 2.0 LANGUAGE Reference page 204

Subclasses of dynamic classes are also dynamic.
Be sure to specify the type when declaring an object, as in the following:
var x:MyClass = new MyClass();
If you do not specify the type when declaring an object (as in the following) then the object is
considered dynamic:
var x = new MyClass();
Availability: ActionScript 2.0; Flash Player 6
Example
In the following example, class
undeclared function on it generates an error at compile time:
class Person2 {
var name:String;
var age:Number;
function Person2(param_name:String, param_age:Number) {
trace ("anything");
this.name = param_name;
this.age = param_age;
}
}
In a FLA or AS file that's in the same directory, add the following ActionScript to Frame 1 on
the Timeline:
// Before dynamic is added
var craig:Person2 = new Person2("Craiggers", 32);
for (i in craig) {
trace("craig." + i + " = " + craig[i]);
}
/* output:
craig.age = 32
craig.name = Craiggers */
204 ActionScript language elements
has not yet been marked as dynamic, so calling an
Person2