> This interface has now been set in stone. Any additions that would be useful for the widget interface, say OnClick(), will require a breaking change This is

> This interface has now been set in stone. Any additions that would be useful for the widget interface, say OnClick(), will require a breaking change This is the expression problem[1]. There is an inherent tension between simplicity of extending the number of operations and simplicity of extending the number of types acted on. [1] https://en.wikipedia.org/wiki/Expression_problem https://en.wikipedia.org/wiki/Expression_problem