The JavaScript exception "return not in function" occurs when a return statement is called outside of a function.

The specularConstant attribute controls the ratio of reflection of the specular lighting. It represents the ks value in the Phong lighting model. The bigger the value the stronger the reflection.

The JavaScript strict mode exception "can't assign to property" occurs when attempting to create a property on primitive value such as a symbol, a string, a number or a boolean. Primitive values cannot hold any property.

The r attribute defines the radius of a circle.

The stop-color attribute indicates what color to use at a gradient stop.

A capturing group groups a subpattern, allowing you to apply a quantifier to the entire group or use disjunctions within it. It memorizes information about the subpattern match, so that you can refer back to it later with a backreference, or access the information through the match results.

The strikethrough-position attribute represents the ideal vertical position of the strikethrough. The strikethrough position is expressed in the font's coordinate system.

The JavaScript warning "reference to undefined property" occurs when a script attempted to access an object property which doesn't exist.

The JavaScript exception "identifier starts immediately after numeric literal" occurs when an identifier started with a digit. Identifiers can only start with a letter, underscore (_), or dollar sign ($).

The await operator is used to wait for a Promise and get its fulfillment value. It can only be used inside an async function or at the top level of a module.