Explain how Refinements work in Ruby, highlighting scoping rules and performance implications.

Refinements provide a localized form of monkey-patching that modifies class behavior strictly within an active lexical scope, avoiding global contamination.

Refinements allow developers to extend or alter core classes safely. Unlike monkey patching, which permanently affects the entire global Ruby process, a refinement is declared within a module wrapper and activated explicitly using using ModuleName. The scope of the modification is strictly lexical, meaning it is only visible until the end of the file, class, or module block where using was declared, preventing leakage into external dependency codebases.