Loadmovie... does a MC "stack" all loaded?

This is kind of a straight-forward question I’ve never known the answer to…

if you have a loadmovie command loading various things into an MC, do those things “stack up” inside the MC or do they get replaced with each successive load? If so, is there a way to “empty” a movieclip before loading something new into it? Maybe that unload command? haha, thanks