Extensions to the built-in Object object.

Because it is dangerous and invasive to augment Object.prototype (i.e., add instance methods to objects), all these methods are static methods that take an Object as their first parameter.

Object is used by Prototype as a namespace; that is, it just keeps a few new methods together, which are intended for namespaced access (i.e. starting with "Object.").

For the regular developer (who simply uses Prototype without tweaking it), the most commonly used methods are probably Object.inspect and, to a lesser degree, Object.clone.

Advanced users, who wish to create their own objects like Prototype does, or explore objects as if they were hashes, will turn to Object.extend, Object.keys, and Object.values.