The less than or equal (<=) operator returns true if the left operand is less than or equal to the right operand, and false otherwise.

The data-* SVG attributes are called custom data attributes. They let SVG markup and its resulting DOM share information that standard attributes can't, usually for scripting purposes. Their custom data are available via the SVGElement interface of the element the attributes belong to, with the SVGElement.dataset property.

The function* keyword can be used to define a generator function inside an expression.

The subtraction assignment (-=) operator performs subtraction on the two operands and assigns the result to the left operand.

The this keyword refers to the context where a piece of code, such as a function's body, is supposed to run. Most typically, it is used in object methods, where this refers to the object that the method is attached to, thus allowing the same method to be reused on different objects.

The JavaScript exception "label not found" occurs when a break or continue statement references a label that does not exist on any statement that contains the break or continue statement.

The JavaScript exception "await expression can't be used in parameter" or "yield expression can't be used in parameter" occurs when the default parameter expression contains the await or yield keyword and has the effect of pausing default parameter evaluation.

The JavaScript exception "is not a non-null object" occurs when an object is expected somewhere and wasn't provided. null is not an object and won't work.

Mutable slice iterator.

Default function parameters allow named parameters to be initialized with default values if no value or undefined is passed.