Cocoa Internals/Extensions
From Lazarus wiki
Extensions are used to add additional lcl-friendly methods to all Cocoa classes. The default implementation of each method should:
- either indicate that a class is not a LCL-specific class (it's Cocoa native) thus should be handled with care
- provide a basic functionality for LCL types (for example setting a control bounds using TRect type. Where cocoa is using float-point NSRect)