DotA 2 Hero Filtering

Question

Real quick question: What are the three rectangles under the "Carry" class at the bottom of the screen?

If you don't understand what I mean, I will add some red circles to where the three rectangles are.

Answer 1

Each hero is given a rating from 0 to 3 in each category, by clicking on the rectangles you can choose to filter heroes with at least 1, at least 2, or 3 "rating" in the category you selected.