The JavaScript exception "invalid date" occurs when an invalid date is attempted to be converted to an ISO date string.

The mask attribute is a presentation attribute mainly used to bind a given <mask> element with the element the attribute belongs to.

The JavaScript exception "Invalid code point" occurs when NaN values, negative Integers (-1), non-Integers (5.4), or values larger than 0x10FFFF (1114111) are used with String.fromCodePoint().

The yChannelSelector attribute indicates which color channel from in2 to use to displace the pixels in in along the y-axis.

This page describes JavaScript's lexical grammar. JavaScript source text is just a sequence of characters — in order for the interpreter to understand it, the string has to be parsed to a more structured representation. The initial step of parsing is called lexical analysis, in which the text gets scanned from left to right and is converted into a sequence of individual, atomic input elements. Some input elements are insignificant to the interpreter, and will be stripped after this step — they include white space and comments. The others, including identifiers, keywords, literals, and punctuators (mostly operators), will be used for further syntax analysis. Line terminators and multiline comments are also syntactically insignificant, but they guide the process for automatic semicolons insertion to make certain invalid token sequences become valid.

The Symbol.unscopables static data property represents the well-known symbol @@unscopables. The with statement looks up this symbol on the scope object for a property containing a collection of properties that should not become bindings within the with environment.

The __proto__ accessor property of Object instances exposes the [[Prototype]] (either an object or null) of this object.

The Object.freeze() static method freezes an object. Freezing an object prevents extensions and makes existing properties non-writable and non-configurable. A frozen object can no longer be changed: new properties cannot be added, existing properties cannot be removed, their enumerability, configurability, writability, or value cannot be changed, and the object's prototype cannot be re-assigned. freeze() returns the same object that was passed in.

The copyWithin() method of Array instances shallow copies part of this array to another location in the same array and returns this array without modifying its length.

The JavaScript exception "cannot use ?? unparenthesized within || and && expressions" occurs when an nullish coalescing operator is used with a logical OR or logical AND in the same expression without parentheses.