Split button pattern - evidence on usability?

1. What is the use of split button?
2. How do you create a split button in HTML?

What is the use of split button?

A split button is a hybrid between a button and a menu: it groups related commands together into a dropdown, but also offers one-click access to a default choice that doesn't require opening the menu.

How do you create a split button in HTML?

Example Explained. Use any element to open the dropdown menu, e.g. a <button>, <a> or <p> element. Use a container element (like <div>) to create the dropdown menu and add the dropdown links inside it. Wrap a <div> element around the button and the <div> to position the dropdown menu correctly with CSS.