The xml:lang attribute specifies the primary language used in contents and attributes containing text content of particular elements.

The for statement creates a loop that consists of three optional expressions, enclosed in parentheses and separated by semicolons, followed by a statement (usually a block statement) to be executed in the loop.

A priority queue implemented with a binary heap.

The JavaScript exception "numbers out of order in {} quantifier" occurs when a quantifier in a regular expression uses the {n,m} syntax but m is less than n.

JavaScript's strict mode is a way to opt in to a restricted variant of JavaScript, thereby implicitly opting-out of "sloppy mode". Strict mode isn't just a subset: it intentionally has different semantics from normal code. Strict mode code and non-strict mode code can coexist, so scripts can opt into strict mode incrementally.

A hash set implemented as a `HashMap` where the value is `()`.

The JavaScript exception "TypeError: already executing generator" occurs when a generator is continued using one of its methods (such as next()) while executing the generator function's body itself.

An IPv6 address.

JavaScript applications consist of statements with an appropriate syntax. A single statement may span multiple lines. Multiple statements may occur on a single line if each statement is separated by a semicolon. This isn't a keyword, but a group of keywords.

The JavaScript exception "precision is out of range" occurs when a number that's outside of the allowed range was passed into toExponential, toFixed, or toPrecision.