The <mask> SVG element defines a mask for compositing the current object into the background. A mask is used/referenced using the mask property and CSS mask-image property.

The y2 attribute is used to specify the second 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 if...else statement executes a statement if a specified condition is truthy. If the condition is falsy, another statement in the optional else clause will be executed.

The JavaScript exception "import declarations may only appear at top level of a module" occurs when an import declaration is not at the top level of a module. This might be because the import declaration is nested in other constructs (functions, blocks, etc.), or more often because the current file is not treated as a module.

The xlink:show attribute indicates how a linked resource should be opened and is meant for XLink-aware processors. In case of a conflict, the target attribute has priority, since it can express a wider range of values.

The JavaScript exception "invalid character in class in regular expression" occurs when a character appears in a v-mode character class but it's not allowed to appear literally.

The let declaration declares re-assignable, block-scoped local variables, optionally initializing each to a value.

The JavaScript exception "missing ) after argument list" occurs when there is an error with how a function is called. This might be a typo, a missing operator, or an unescaped string.

The repeatCount attribute indicates the number of times an animation will take place.

The try...catch statement is comprised of a try block and either a catch block, a finally block, or both. The code in the try block is executed first, and if it throws an exception, the code in the catch block will be executed. The code in the finally block will always be executed before control flow exits the entire construct.