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 Object.seal() static method seals an object. Sealing an object prevents extensions and makes existing properties non-configurable. A sealed object has a fixed set of properties: new properties cannot be added, existing properties cannot be removed, their enumerability and configurability cannot be changed, and its prototype cannot be re-assigned. Values of existing properties can still be changed as long as they are writable. seal() returns the same object that was passed in.

The Object.fromEntries() static method transforms a list of key-value pairs into an object.

The toString() method of BigInt values returns a string representing the specified BigInt value. The trailing "n" is not part of the string.