Radom Color Generator

I was reading this tutorial titled as [COLOR=“Green”]Random Color[/COLOR] (http://www.kirupa.com/developer/flash5/randomcolor.htm)in the Flash tutorials, Advance Script section. I have a few questions.

In the tutorials it has parts like:

[COLOR=“Blue”]_root[[COLOR=“green”]“r”[/COLOR]+myNum+[COLOR=“Green”]“Diff”[/COLOR]][/COLOR]
[COLOR=“blue”]_root[[COLOR=“green”]“r”[/COLOR]+myNum+[COLOR=“green”]“New”[/COLOR]][/COLOR]
[COLOR=“blue”]_root[[COLOR=“green”]“r”[/COLOR]+myNum+[COLOR=“green”]“Change”[/COLOR]][/COLOR]

are the “r”, “Diff”/“New”/“Change” defined in the Object class?
how does flash know what is “r” = red, “b” = blue, “g” = green and the meanings of “Diff”, “New” etc.

Secondly, do the square brackets mean anything? Is that what makes flash understands the weird things mentioned in the above question?

Thank you very much