Accessing root for .as file

I have searched extensively, so please accept my apologies if this has already been answered.

I am trying to call a function in my main FLA from an .as file. The situation is like this:

Main FLA includes an .as file which itself includes a second .as file:

Main -> .as -> .as

I wish to make the function call from the second .as file but I do not know how to address it. I seem to be able to address other items in the main FLA such as:

[COLOR=Blue]_root[/COLOR].testText.[COLOR=Blue]text[/COLOR] = "found main from .as";

which works, whereas the following does not:

[COLOR=Blue]_root[/COLOR].testFunction(testVar);

I think I must have missed something very basic, I appreciate any help. Thanks.

Al