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.

`Error` is a trait representing the basic expectations for error values, i.e., values of type `E` in `Result<T, E>`.

Representation of a borrowed C string.

A mutable iterator over the values of a `HashMap`.

An iterator over the values of a `HashMap`.

The function* declaration creates a binding of a new generator function to a given name. A generator function can be exited and later re-entered, with its context (variable bindings) saved across re-entrances.

The y1 attribute is used to specify the first y-coordinate for drawing an SVG element that requires more than one coordinate. Elements that only need one coordinate use the y attribute instead.

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.

The JavaScript exceptions "unexpected token" occur when the parser does not see a token it recognizes at the given position, so it cannot make sense of the structure of the program. This might be a simple typo.

The refX attribute defines the x coordinate of an element's reference point.