Without knowing the specifics, the best answer I can come up with here is that it's Javascript -- so yeah, you can write it affect parts of the page, or all of the page. You can have it control just the navigation bar on a site, or the whole site altogether.

There are caveats here -- if you have the library loaded from any page with html5 location mode enabled, it'll take over link-handling on those pages. With Angular, it's easy to circumvent by adding a 'target' attribute to the links, but on a legacy site, that might mean having to touch every page that Angular doesn't already exist on, which would be a chore.

The alternative is to not enable HTML5 location mode (so links are to #/link/) or to adjust the targets on links that aren't meant to be handled by JS.

All summed up though, while it may not be written anywhere, I've always gotten the feeling that Angular prefers to own the entire page, loading partials into views where appropriate, and using separate controllers for other portions of the page. That said, it can work either way, but does take some extra special care.