Accessibility: add aria-expanded attribute to menu button(s)

[adamjohnson]

Request:

Priority navigation should add aria-expanded to the <button> tag(s)—for both "More" and the breakpoint mobile menu:

What is aria-expanded?

aria-expanded indicates whether the element, or another grouping element it controls, is currently expanded or collapsed.

W3 aria-expanded spec

Current markup:

<button aria-controls="menu" class="nav__dropdown-toggle priority-nav__dropdown-toggle priority-nav-is-visible" prioritynav-count="2">more</button>

Proposed markup:

<button aria-expanded="false" aria-controls="menu" class="nav__dropdown-toggle priority-nav__dropdown-toggle priority-nav-is-visible" prioritynav-count="2">more</button>

aria-expanded is a boolean attribute. When the menu is open, it should toggle to true.

Here's a demo that shows aria-expanded in action in a similar context.