Easily create classes with rich, declarative attributes - Parameter objects - that include extended metadata for various purposes such as runtime type and range validation, documentation strings, default values or factories, nullability, etc. In this sense, Param is conceptually similar to libraries like Pydantic, Python's dataclasses, or Traitlets. A suite of expressive and composable APIs for reactive programming, enabling automatic updates on attribute changes, and declaring complex reactive dependencies and expressions that can be introspected by other frameworks to implement their own reactive workflows.