The JavaScript warning "-file- is being assigned a //# sourceMappingURL, but already has one." occurs when a source map has been specified more than once for a given JavaScript source.

Iteration protocols aren't new built-ins or syntax, but protocols. These protocols can be implemented by any object by following some conventions.

The xlink:title attribute is used to describe the meaning of a link or resource in a human-readable fashion.

The y attribute defines a y-axis coordinate in the user coordinate system.

The JavaScript exception "WeakSet key (or WeakMap value) 'x' must be an object or an unregistered symbol" occurs when a value of invalid type is used as a key in a WeakSet or as a value in a WeakMap.

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

Trailing commas (sometimes called "final commas") can be useful when adding new elements, parameters, or properties to JavaScript code. If you want to add a new property, you can add a new line without modifying the previously last line if that line already uses a trailing comma. This makes version-control diffs cleaner and editing code might be less troublesome.

A disjunction specifies multiple alternatives. Any alternative matching the input causes the entire disjunction to be matched.

The JavaScript exception "Permission denied to access property" occurs when there was an attempt to access an object for which you have no permission.

The side attribute determines the side of a path the text is placed on (relative to the path direction).