Marks this element as a navigational container, such as a menu or navigation bar.
When a link within an [up-nav] element points to its layer's location,
it is assigned the .up-current class. When the browser navigates to another location, the class is removed automatically.
See Navigation bars for details and examples.
Example
Let's look at a simple menu with two links:
<div up-nav> <!-- mark: up-nav -->
<a href="/foo">Foo</a>
<a href="/bar">Bar</a>
</div>
When the browser location changes to /foo, the first link is marked as .up-current:
<div up-nav>
<a href="/foo" class="up-current">Foo</a> <!-- mark: up-current -->
<a href="/bar">Bar</a>
</div>
When the browser location changes to /bar, the first link loses its .up-current class.
Now the second link is marked as .up-current:
<div up-nav>
<a href="/foo">Foo</a>
<a href="/bar" class="up-current">Bar</a> <!-- mark: up-current -->
</div>
