Blizzard Addons and refernecing their frames...

[Inokis]

I'm having trouble understanding how to reference the blizzard addons frames since they use them in the .pub format.

Before I could just use :
local MacroFramelevel = MacroFrame:GetFrameLevel();
Now I get an error:
'MacroFrame' (a nil value)

What is the process now of referencing these frames so that I can keep other things from hiding these frames?