That design choice leaves your fingers free for mouse - style click buttons, plus smartly - placed browser buttons that leave your thumb on the ball. (digitaltrends.com)
And the most important point is the required navigational functions do not conflict with standard browser buttons in name, icon, or function. (elearningindustry.com)
The standard also specifies that navigational functions should not conflict with standard browser buttons in terms of name, display, or function. (elearningindustry.com)