Which of the following is not typically a characteristic of mixin classes?

Mixin classes are a design pattern used in object-oriented programming to provide additional functionality to classes without having to create a common superclass. They typically serve to enhance or add behaviors to other classes through multiple inheritance.

The characteristic of mixin classes not typically being intended for direct instantiation is crucial for understanding their role in design patterns. Rather than being instantiated on their own, mixins are meant to be combined with other classes. This allows them to impart methods and attributes to those other classes, supporting the primary goal of facilitating code reuse and enhancing functionality in a modular fashion.

The function of providing additional functionality, reducing code duplication, and facilitating code reuse across different classes are all key attributes of mixins. They allow developers to keep their codebase DRY (Don't Repeat Yourself) by reusing shared behaviors across multiple classes. Therefore, the correct choice highlights the unique nature of mixin classes in that they are designed to be utilized by other classes rather than existing independently.