It's infeasible for the browser to know "what you see" in the general case. What if the text was in position, but very small and almost the same color as the b

It's infeasible for the browser to know "what you see" in the general case. What if the text was in position, but very small and almost the same color as the background? Does the browser need to know if you're red-green colour blind? If you're farsighted?