I believe the "input box" is a progress bar.
The checkboxes toggle the selection by ranking and color, respectively.
To see how this works, open a contact sheet and rank some photos 1, 2, 3, 4, and 5. Next, click on the 0* (zero star), 1*, 2*, etc. and see how the display changes. Now, click on the checkbox to the left of the stars and see the change.
Deven