User lands on the page, and presses Tab.
User presses Enter to navigate within the pager area.
User presses Tab or the right arrow key to move the cursor to the next item within the pager area.
User tabs to page link 20 and presses Enter. Page 20 loads, and the focus is on page link 21. This is because the number 20 is no longer available as a link. Otherwise the focus should stay on the item last selected by the user. For example, if the user placed focus on the "next >" link and pressed enter, the focus should be placed on the next > link when the next page loads, as long as there is a next page. If there isn't a next page, focus would be placed on the "< previous" link.
User tabs to the page size dropdown.
User presses Enter. The focus is placed on the current value by default.
User presses the up arrow key to put the focus on 10.
User presses Enter. Now the page displays 10 items per page. The focus is placed on the dropdown.