HitTest clips in clips?

hi, i’m making a platformer and people told me the way to make it was to have the bg move, not the player. (thx bluemagica and the other dude, who I forget your name). Is there a way to put everything in the same clip, or do i have to have one for the background, one for the platformers, one for the special blocks etc…?

thanks,
Press_Tilty