How to set breakpoints in an as3 class ?

[rivella50]

Hi there,

i've just installed Flex Builder 2.0.1 and wanted to test the debugging
feature by trying to set some breakpoints in the following class Main.as:


package {
import flash.display.Sprite;
import flash.text.TextField;

public class Main extends Sprite {

public function Main() {
var display_txt:TextField = new TextField();
display_txt.text = "Hello World!";
addChild(display_txt);
}
}
}


The application compiles and shows up in the browser's loaded .swf,
but i cannot set any breakpoints in that class.

Can someone please tell me what i have to do ? Do i have to enable
the debug feature somewhere ?
In an .mxml file i can set breakpoints, but currently i don't want to
use such a description file.

Thank you.
rivella50