"does that apply to setting a URL path?"
No. when using getURL, it always looks in the root folder..
so if your site is in a folder that is in a folder in the root
directory, and you want to go to a page that is just in one folder
in the root directory, just use getURL("folder/page.html");
"different layers of a movie clip"
No. If you have a Move Clip on the main timeline, using
_parent. will access the root timeline. If you are in a Movie Clip
that is in a Movie Clip, using _parent. will access the Movie Clip
one level up.