The target attribute should be used when there are multiple possible targets for the ending resource, such as when the parent document is embedded within an HTML or XHTML document, or is viewed with a tabbed browser. This attribute specifies the name of the browsing context (e.g., a browser tab or an (X)HTML iframe or object element) into which a document is to be opened when the link is activated:

Inspects an environment variable at compile time.

A character class matches any character in or not in a custom set of characters. When the v flag is enabled, it can also be used to match finite-length strings.

The JavaScript exception "must call super constructor before using 'this' in derived class constructor" occurs when the super() is not called for a given derived class constructor, and the derived constructor tries to access the value of this, or the derived constructor has already returned and the return value is not an object.

The JavaScript exception "SyntaxError: private fields can't be deleted" occurs when delete is used on a private property of a class or an object.

A type that is composed of other types.

The JavaScript exception "unlabeled break must be inside loop or switch" occurs when a break statement is not inside a loop or a switch statement.

The JavaScript exception "duplicate capture group name in regular expression" occurs when a regular expression pattern contains two or more named capturing groups with the same name, and these capture groups could be matched at the same time.

Constructs parameters for the other string-formatting macros.

The opacity attribute specifies the transparency of an object or of a group of objects, that is, the degree to which the background behind the element is overlaid.