attachMovie() > Linkdage > ?AS 2.0 classes?

Flash 8
Actionscript 2.0

Hi there
I am trying to build a flash game. So I need to use the attachMovie() code. The problem is that when I click on the linkage of the movieclip of a rocket, I have to fill in a box called “AS 2.0 classes”. So what should I fill it in with?

Thank you.