A CheckMenuItem is a menu item that maintains the state of a boolean value in addition to a MenuItem usual role in activating application code.
A check box indicating the state of the boolean value is displayed at the left side of the MenuItem. Activating the MenuItem toggles the value.
menuitem
├── check.left
╰── <child>
nuItem has a main CSS node with
name menuitem, and a subnode with name check, which gets the .left or .right style class.