MovieClip-derived object not appearing?

Okay, I’ve got an attachMovie clip of some sort to appear, but it doesn’t seem to be of the type I want it.

I’m really, really confused about that last optional parameter of attachMovie, which seems key to the whole idea. The code from the tutorial here:

http://www.kirupa.com/developer/oop2/AS2OOPInheritance4.htm

has the “InitObject” written in brackets, with a call to a function in that Object’s class definition after the statement(?!). Yet other documentation (the AS dictionary on MM’s site) has it in square brackets. Can someone explain exactly how the whole InitObject thing works? What’s the syntax, and when it is necessary and not necessary?

(Thanks for the help so far, Senocular!)