When you call _root.getBytesTotal() does that return absolutely all the bytes in the whole thing?

im quite new to this so sorry if im not making sense.
say i had a separate movie clip on one frame, will it then look inside that movie clip and count all the bytes inside that or does it only count the bytes on the first timeline thing.

if you get that please help, i dont think my preloader is loading everything even though getBytesLoaded() returns 100%