An object initializer is a comma-delimited list of zero or more pairs of property names and associated values of an object, enclosed in curly braces ({}). Objects can also be initialized using Object.create() or by invoking a constructor function with the new operator.

The elevation attribute specifies the direction angle for the light source from the XY plane towards the Z-axis, in degrees. Note that the positive Z-axis points towards the viewer of the content.

The remainder (%) operator returns the remainder left over when one operand is divided by a second operand. It always takes the sign of the dividend.

The end attribute defines an end value for the animation that can constrain the active duration.

The async function keywords can be used to define an async function inside an expression.

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

A WeakMap is a collection of key/value pairs whose keys must be objects or non-registered symbols, with values of any arbitrary JavaScript type, and which does not create strong references to its keys. That is, an object's presence as a key in a WeakMap does not prevent the object from being garbage collected. Once an object used as a key has been collected, its corresponding values in any WeakMap become candidates for garbage collection as well — as long as they aren't strongly referred to elsewhere. The only primitive type that can be used as a WeakMap key is symbol — more specifically, non-registered symbols — because non-registered symbols are guaranteed to be unique and cannot be re-created.

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

The super keyword is used to access properties on an object literal or class's [[Prototype]], or invoke a superclass's constructor.

The yield operator is used to pause and resume a generator function.