The optional chaining (?.) operator accesses an object's property or calls a function. If the object accessed or function called using this operator is undefined or null, the expression short circuits and evaluates to undefined instead of throwing an error.

The decoding attribute, valid on <image> elements, provides a hint to the browser as to whether it should perform image decoding along with rendering other content in a single presentation step that looks more "correct" (sync), or render and present the other content first and then decode the image and present it later (async). In practice, async means that the next paint does not wait for the image to decode.

The <metadata> SVG element adds metadata to SVG content. Metadata is structured information about data. The contents of <metadata> should be elements from other XML namespaces such as RDF, FOAF, etc.

The <switch> SVG element evaluates any requiredFeatures, requiredExtensions and systemLanguage attributes on its direct child elements in order, and then renders the first child where these attributes evaluate to true.

The right shift assignment (>>=) operator performs right shift on the two operands and assigns the result to the left operand.

The strict equality (===) operator checks whether its two operands are equal, returning a Boolean result. Unlike the equality operator, the strict equality operator always considers operands of different types to be different.

A named backreference refers to the submatch of a previous named capturing group and matches the same text as that group. For unnamed capturing groups, you need to use the normal backreference syntax.

A UDP socket.

The font-size-adjust attribute allows authors to specify an aspect value for an element that will preserve the x-height of the first choice font in a substitute font.

The height attribute defines the vertical length of an element in the user coordinate system.