Bootstrap creator here.
* .navbar is for positioning/sizing.
* .navbar-inner is required for the gradient because `overflow: visible;` is not respected by IE when `filter` is present.
* .container is for centering the content within the navbar
No idea what .navbar-content is—that's not part of the Bootstrap navbar component. We also use a `ul.nav`, not `div.nav`.
So, close to the core, but not 100%.